Some people want to scare their friends, so they get them into some rediculous situation that is scary. I've seen it a few times, and I dont really like the idea of it. Scaring someone really badly is not nice.
i.e.
Girl gets asked to do a temp job as a secretary by one of her friends, the boss says she just broke up with her boyfriend and he was really pissed, then as the girl is working at the front desk the boyfriend comes in and 'stabs' the boss. Then the girls friend runs in and is like you are on scare tactics! You just got punk'd!
Not really funny, and very mean.