Boludo
This is probably the most used argentinian word.
At first it was just a noun, to say to somone that he was really stupid, but now, you can use it to call your pal in a friendly way.
Is used for a lot of things, and it has become a verbe: BOLUDEAR; in spanish, the conjuation will be YO boludeo, TU boludeas, EL boludea, NOSOTROS boludeamos, ELLOS boludean. Basicly means that you are not doing nothing.
Also, in Argentina, this word is used to say you are mocking someone, using irony to make the other one looked like a stupid. The quivalent for the english "are you making fun of me?" "me estas boludeando?"
Que haces boludo!? Todo bien?!
What's up boludo? All rigth?

Sos un boludo terrible, la jodiste!
You are a terrible boludo, you fucked it!

-Que estabas haciendo?
-Nada, boludeando.
-What wwere you doing?
-Nothing, boludeando(doing nothing)