On the old site, the moderator discussed the difference between jokes and leitzanus:
When I was in a certain Yeshiva, every year on Purim some bochurim would do a Purim Shpiel. In the shpiel they would mimic the Rebbeim's voices, mannerisms, talking style, etc. It was very funny. But now I'm concerned: Is it considered leitzanus? After watching the shpiel, isn't it very possible that bochurim will not take the words of their Rebbeim as seriously during the rest of the year?
It depends how it's done. I wasn't there and I don't know enough about what happened to judge a particular Metzius, but there is no question that if in fact the Rebbaim were portrayed in a way that their honor would be lessened in the eyes of any of the students, then yes, it was Letzonus. And if It was done in a disrespectful manner it was also humiliating the Rebbeim in public.