What are the negative consequences of slacking off after attaining tenure? As I was thinking about the question
Can I slack off and get a PhD?,
I realized that I wanted to say in my answer


  If you want to slack off,
  the best time to do so is after you have received tenure
  as a college professor,
  because at that point you can't be fired
  except for egregious offences.


I am not yet even an assistant professor,
so I don't know whether the statement above is really true.

Question:
What could the negative consequences be
for a professor who has just received tenure,
if he were to put in the bare minimum effort needed in teaching
just to achieve average teaching performance,
and were to just stop doing research and publishing papers?

Note:
I don't plan to slack off if I were in the future
able to get a tenured position,
but I am just curious what happens to those professors who do.
I think the first question is, what does "slack off" really mean?  Many professors do change their priorities after tenure for a slower paced approach to their work more in line with their own intellectual values.  Many things that might be perceived as "slacking off" in a pre-tenure professor actually do have value and are much easier to pursue post-tenure, e.g., dedicating more time to students and teaching rather than research, or taking a slower pace to try to figure out an angle on deeper and harder to address issues.

But let's assume that our hypothetical professor is just saying, "I got mine, and I'm going to do the absolute minimum hereafter!"  Here are some of the non-firing consequences:


Not getting grants, it will be hard to have students.
Their professional prestige will plummet, and anything they do want to do will get harder.
They may get stuck with unpleasant scut-work tasks for the department, and will have more responsibilities foisted on them because "they have the time" that their harder working colleagues do not.
They will not get promotion to higher academic ranks, nor the accompanying pay rises.


Some people may actually be comfortable with this, and having a person who's given up ambition and embraced a comfortable position as the organization's reliable clean-up detail can actually be a good thing, as it takes those tasks away from others who have more ambition.

But what if the slacker professor really doesn't care, and does a poor (but not quite enough to be fired) job at all the tasks they are assigned by the department?
Well, every organization has ways to make a person's life hell without firing them.  In the next departmental reorganization, the slacker professor might find themselves getting moved to a small lightless basement office, the administrative staff may ignore requests for assistance, colleagues may simply treat the person as a pariah.  Few people last long in an actively hostile workplace, and it may be harder to fire a person than to make them quit...