Question: I deleted an old answer that had a -3 score, and didn't get a peer pressure badge.

If it's not intended to be awarded more than once, it loses its reason to be, that is encouraging people to delete (what the community considers) bad posts.

Should it be awarded more than once or not? If it is, could it become like the [troll cap](http://37signals.com/svn/archives2/introducing_the_troll_cap.php)?

Answer: 
It's awarded just once. I'm tempted to say it should be awarded for each -3 post you delete, but I'm not so sure that's something we want to celebrate more often.
[It's not awarded more than once](https://meta.stackexchange.com/questions/10026/which-badges-are-awarded-only-once). It's also one of those badges that aren't awarded instantly, but rather seem to be awarded on a batch basis some minutes to hours later.

I don't really see the value in awarding this one more than once -- it corresponds more to a particular behaviour that you have done, rather than corresponding to a particular question or answer (as the multiply-awarded badges do).