By saying that you're imposing your sense of humor on others too (as in, the prankster's sense of humor is "pranks are funny"; your sense of humor is "pranks are not funny"; according to your comment your stance is that pranks shouldn't be tolerated). You don't have to laugh, and you're free to say you don't like pranks. But tolerating other people's opinions/sense of humor/whathaveyou seems like basics to me.
(Maybe we just have different experiences and thus different definitions of the word.)