user5711: Bodybuilding and powerlifting are making us stronger and more manliness, body can produce more testosterone and we're generally healthier. Yes, there are some bad things about this like anabolics or synthol, but in general - can someone who trains with weights become buddhist? Are they too agressive in eyes of buddhists?

user-1: With right intention, bodybuilding can be used as a tool to practice wholesome activities, in lieu of more impermanent, less wholesome activities. For example:

A welcoming towards what is normally perceived as negative feelings or vedanā with hard physical training or dieting and deprivation. (FYI: the Zazen Yojinki says you should eat two-thirds of your capacity.)
Lifting heavy weights as an exercise of vitakka and vicara.
Enforcing a wholesome routine which strengthens the body. (It has been said that the body is the physical aspect of the mind.)

Mileage may vary depending upon your definition of bodybuilding. Yours assumes aggression as a prerequisite. 

user254: Since you ask, "What buddhism says", one quote which might be relevant is from the Puttamansa Sutta (SN 12.63), which I think recommends what's the appropriate attitude to have towards food:

How, O monks, should the nutriment edible food be considered?
...
What do you think, O monks? Will they eat the food for the pleasure of it, for enjoyment, for comeliness' sake, for (the body's) embellishment?"[7]
"Certainly not, O Lord.

The corresponding quote from the Visuddhimagga,

Reflecting
  wisely, he uses alms food neither for amusement nor for intoxication nor for
  smartening nor for embellishment, but only for the endurance and continuance of
  this body, for the ending of discomfort, and for assisting the life of purity:

‘Thus I
    shall put a stop to old feelings and shall not arouse new feelings, and I shall be
    healthy and blameless and live in comfort.’


Or from the Bhikkhuni Sutta (AN 4.159),


'This body, sister, comes into being through food. And yet it is by relying on food that food is to be abandoned.'

Thus was it said. And in reference to what was it said? There is the case, sister, where a monk, considering it thoughtfully, takes food — not playfully, nor for intoxication, nor for putting on bulk, nor for beautification — but simply for the survival & continuance of this body, for ending its afflictions, for the support of the holy life, [thinking,]

'Thus will I destroy old feelings [of hunger] and not create new feelings [from overeating]. I will maintain myself, be blameless, & live in comfort.'

Then he eventually abandons food, having relied on food.

'This body, sister, comes into being through food. And yet it is by relying on food that food is to be abandoned.'

Thus was it said, and in reference to this was it said.

The above are addressed to monks (see also Thiago's answer). In answer to, "can someone who trains with weights become buddhist", I suppose it would be abnormal for a Buddhist monk to be a "body-builder" ... maybe an ambition like "become more manly" is a kind of conceit, where the intention is to beautify the body ... not exactly immoral but not really on-topic as far as a monk is concerned.
On the other hand, some monks do (or have done) physical work: helping to build things using concrete, etc.
And I think that (most?) monks do tend to have some physical exercise in their daily routine: especially walking (or, prostrations); whether it's walking on alms-round each morning, walking meditation, even (in the case of the Dalai Lama) walking on a tread-mill. So some endurance exercise (or "building the body" for endurance even if not to look muscle-bound, or "maintaining" the body even if not "building" it) isn't incompatible with even a monk's life.

user-1: These practices are seeing just like any other sport that does not involve morally problematic activities like killing or hurting other beings: it's just a sport. I don't think power lifters et al. are seen as aggressive -- not like, say, bullfighting or any other blood sport. 
But things might be different for a buddhist body builder or power lifter. In the buddhist training, there is a spectrum from lay to monastic, and in that spectrum, the inclination to engage in certain activities change.
For example, a lay buddhist might take to heart five buddhist precepts:

I undertake the training rule to abstain from killing.
I undertake the training rule to abstain from taking what is not given. 
I undertake the training rule to avoid sensual misconduct.
I undertake the training rule to abstain from false speech. 
I undertake the training rule to abstain from fermented drink that causes heedlessness.

These are among the most basic buddhist training rules that enables one to practice buddhism and none has anything to say about body building  -- or sports for that matter (but drugs that cause heedlessness are breaking the fifth, which may obstruct the person's practice). So, lay buddhists can normally practice sports like body building etc. One of the main points of evaluation is ethical conduct and many sports do not present an ethical problem.
Now, a more committed lay buddhist might take some extra precepts, like:
I undertake to abstain from singing, dancing, playing music, attending entertainment performances, wearing perfume, and using cosmetics and garlands (decorative accessories).
Taking that vow likely conflicts with watching and participating on competitions. Even though, strictly speaking, it might not be a problem if one just wants to practice the sport, a person more committed to buddhist training might be less inclined to partake in activities that might hurt his or her buddhist training progress.
In the end of the spectrum there's the monk or nun. They are unlikely to devote themselves to activities that require too much (of time, energy, money, etc) and that do not benefit / or creates obstacles to their buddhist practice.

5711: <p>Bodybuilding and powerlifting are making us stronger and more manliness, body can produce more testosterone and we're generally healthier. Yes, there are some bad things about this like anabolics or synthol, but in general - can someone who trains with weights become buddhist? Are they too agressive in eyes of buddhists?</p>
 -1: <p>With right intention, bodybuilding can be used as a tool to practice wholesome activities, in lieu of more impermanent, less wholesome activities. For example:</p>

<ul>
<li><p>A welcoming towards what is normally perceived as negative feelings or vedanā with hard physical training or dieting and deprivation. (FYI: the <a href="https://books.google.com/books?id=97xCAgAAQBAJ&amp;lpg=PA44&amp;dq=zazen%20yojinki%20%22two-thirds%22&amp;pg=PA44#v=onepage&amp;q=zazen%20yojinki%20%22two-thirds%22&amp;f=false" rel="nofollow">Zazen Yojinki says</a> you should eat two-thirds of your capacity.)</p></li>
<li><p>Lifting heavy weights as an exercise of vitakka and vicara.</p></li>
<li>Enforcing a wholesome routine which strengthens the body. (It has been said that the body is the physical aspect of the mind.)</li>
</ul>

<p>Mileage may vary depending upon your definition of bodybuilding. Yours assumes aggression as a prerequisite. </p>
 254: <p>Since you ask, "What buddhism says", one quote which might be relevant is from the <a href="http://www.accesstoinsight.org/tipitaka/sn/sn12/sn12.063.nypo.html" rel="nofollow noreferrer">Puttamansa Sutta (SN 12.63)</a>, which I think recommends what's the appropriate attitude to have towards food:</p>

<blockquote>
  <p>How, O monks, should the nutriment edible food be considered?</p>
  
  <p>...</p>
  
  <p>What do you think, O monks? Will they eat the food for the pleasure of it, for enjoyment, for comeliness' sake, for (the body's) embellishment?"[7]</p>
  
  <p>"Certainly not, O Lord.</p>
</blockquote>

<p>The corresponding quote from the <a href="http://www.accesstoinsight.org/lib/authors/nanamoli/PathofPurification2011.pdf" rel="nofollow noreferrer">Visuddhimagga</a>,</p>

<blockquote>
  <p>Reflecting
  wisely, he uses alms food neither for amusement nor for intoxication nor for
  smartening nor for embellishment, but only for the endurance and continuance of
  this body, for the ending of discomfort, and for assisting the life of purity:</p>
  
  <blockquote>
    <p>‘Thus I
    shall put a stop to old feelings and shall not arouse new feelings, and I shall be
    healthy and blameless and live in comfort.’</p>
  </blockquote>
</blockquote>

<p>Or from the <a href="http://www.accesstoinsight.org/tipitaka/an/an04/an04.159.than.html" rel="nofollow noreferrer">Bhikkhuni Sutta (AN 4.159)</a>,</p>

<blockquote>
  <blockquote>
    <p>'This body, sister, comes into being through food. And yet it is by relying on food that food is to be abandoned.'</p>
  </blockquote>
  
  <p>Thus was it said. And in reference to what was it said? There is the case, sister, where a monk, considering it thoughtfully, takes food — not playfully, nor for intoxication, nor for putting on bulk, nor for beautification — but simply for the survival &amp; continuance of this body, for ending its afflictions, for the support of the holy life, [thinking,]</p>
  
  <blockquote>
    <p>'Thus will I destroy old feelings [of hunger] and not create new feelings [from overeating]. I will maintain myself, be blameless, &amp; live in comfort.'</p>
  </blockquote>
  
  <p>Then he eventually abandons food, having relied on food.</p>
  
  <blockquote>
    <p>'This body, sister, comes into being through food. And yet it is by relying on food that food is to be abandoned.'</p>
  </blockquote>
  
  <p>Thus was it said, and in reference to this was it said.</p>
</blockquote>

<p>The above are addressed to monks (see also <a href="https://buddhism.stackexchange.com/a/10804/254">Thiago's answer</a>). In answer to, "can someone who trains with weights become buddhist", I suppose it would be abnormal for a Buddhist <em>monk</em> to be a "body-builder" ... maybe an ambition like "become more manly" is a kind of conceit, where the intention is to beautify the body ... not exactly immoral but not really on-topic as far as a monk is concerned.</p>

<p>On the other hand, some monks do (or have done) physical work: helping to build things using concrete, etc.</p>

<p>And I think that (most?) monks do tend to have some physical exercise in their daily routine: especially walking (or, <a href="http://providencezen.org/why-we-bow-108-prostrations" rel="nofollow noreferrer">prostrations</a>); whether it's walking on alms-round each morning, walking meditation, even (in the case of the Dalai Lama) walking on a tread-mill. So some endurance exercise (or "building the body" for endurance even if not to look muscle-bound, or "maintaining" the body even if not "building" it) isn't incompatible with even a monk's life.</p>
 -1: <p>These practices are seeing just like any other sport that does not involve morally problematic activities like killing or hurting other beings: it's just a sport. I don't think power lifters et al. are seen as aggressive -- not like, say, <a href="https://en.wikipedia.org/wiki/Bullfighting" rel="nofollow">bullfighting</a> or any other blood sport. </p>

<p>But things might be different for a buddhist body builder or power lifter. In the buddhist training, there is a spectrum from lay to monastic, and in that spectrum, the inclination to engage in certain activities change.</p>

<p>For example, a lay buddhist might take to heart <a href="http://www.accesstoinsight.org/lib/authors/bodhi/wheel282.html#prec" rel="nofollow">five buddhist precepts</a>:</p>

<ol>
<li><em>I undertake the training rule to abstain from killing.</em></li>
<li><em>I undertake the training rule to abstain from taking what is not given.</em>   </li>
<li><em>I undertake the training rule to avoid sensual misconduct.</em></li>
<li><em>I undertake the training rule to abstain from false speech.</em>   </li>
<li><em>I undertake the training rule to abstain from fermented drink that causes heedlessness.</em></li>
</ol>

<p>These are among the most basic buddhist training rules that enables one to practice buddhism and none has anything to say about body building  -- or sports for that matter (but drugs that cause heedlessness are breaking the fifth, which may obstruct the person's practice). So, lay buddhists can normally practice sports like body building etc. One of the main points of evaluation is ethical conduct and many sports do not present an ethical problem.</p>

<p>Now, a more committed lay buddhist might take some extra precepts, like:</p>

<p><em>I undertake to abstain from singing, dancing, playing music, attending entertainment performances, wearing perfume, and using cosmetics and garlands (decorative accessories).</em></p>

<p>Taking that vow likely conflicts with watching and participating on competitions. Even though, strictly speaking, it might not be a problem if one just wants to practice the sport, a person more committed to buddhist training might be less inclined to partake in activities that might hurt his or her buddhist training progress.</p>

<p>In the end of the spectrum there's the monk or nun. They are unlikely to devote themselves to activities that require too much (of time, energy, money, etc) and that do not benefit / or creates obstacles to their buddhist practice.</p>
