Many yeshivas run skits during Purim in which they poke fun at the rabbis at the yeshiva (at their quirks, mannerisms, or maybe even their dei’os). Isn’t this considered loshon hara? Moreover, isn’t this loshon hara b’rabim? How is this such a widespread custom?
The main issue here is that, although it is done as “Purim fun” it is embarrassing the Rabbis in public which is a very serious sin. It used to be done more, however it has been stopped in many places. Especially since there were a number of stories where, some student embarrassed the Rosh Yeshiva, and they had serious problems later on in life.