I don't want to necessarily contend that trolling is "good," but I think it can be done in a way that is healthy. I liken it to in college, when there is that one dude who's way-too-serious and so you play a practical joke on him/her to get them to cool their jets. For example, in college there was this kid Chris, and he printed schoolwork in the psychology lab printers and was always TERRIFIED they'd get mad at him for doing so (you were only allowed to print schoolwork related to psychology on those printers). So one day a few friends printed out an official-looking notice that he was in serious trouble for doing so, and that he had to pay a fine of $23.35 and slipped it into his campus mailbox.
Now you may think I'm just a jerk for this, and maybe I am, but for me this act was an olive-branch. If he had laughed it off and called me a "fucker" he would have been more a friend. I think when somebody is overlysensitive to something your friends can sometimes intentionaly desensitize you by bringing it up too much as a way to relax your trigger (say your roommate is afraid of snakes so you put a rubber snake in their bed).
Now I have no idea if other people who do this kind of thing do it with good intent or not, and it's entirely possible that Chris hates me more than ever and is even more paranoid about following silly rules. But I can say that I at least consider this type of thing a potential bonding activity.