Each theatre or theatre company is different, naturally. But it seems to me that community theatres are rife with pranksters. The worst kind of them being those who strike at performers while on stage.
Perhaps there is something in the nature of those who are passionate about theatre that makes them more likely to engage in prankdom. Perhaps it is a way to relieve high levels of tension and stress that live theatre can bring. Maybe it is the chance of a prank throwing someone off their game while in front of a live audience. It could be neither of these things.
Whatever the reason, I must be a spoiled sport on this one. Though I have never been the victim of a prank, I have to, in most cases, stand in opposition to doing so, when it comes to theatre performances.
To begin with, the audience, who has usually paid money to watch a group of actors perform, are not in on the joke. If said joke or prank has a decent chance of affecting an actor's performance in the scene, (and that is generally the idea), it is unfair to ticket holders. Why should they product they pay for be lessoned in quality just because you thought it would be funny? To do so indicates a lack of dedication to the production as a whole.
Recall I did say I was opposed "in most cases". If you are very familiar with the person being pranked, and can be certain they will not be thrown off of their performance by what you have done, the occasional tom foolery may be acceptable. Even then , however, it should not be anything that affects the blocking of the play, the ability to hear one's cue, or throw off the audience's understanding of the scene. (Writing goofy messages, or weird faces on pieces of paper that have to be handled, but not read, by an actor is a famous example where I come from.)
To be safe though, these kind of antics, if you must succumb to them, should be reserved for late, pre-technical rehearsals. Or during pick-up rehearsals between weekends. That way the central focus of any show, the audience, does not have to pay for your inside joke.