I am not a fan of practical jokes. They are often cruel rather than amusing and it is not fun when one person is the victim and is being laughed at by others. Sometimes they can be excused because they cause just minor embarrassment but this too is dangerous because what can seem like something minor to the perpetrators can be traumatic for the victim.
Sometimes people go to extraordinary lengths to play such pranks. Take this example from Brazil (it looks like for a Candid Camera-like TV show) where people construct a fake elevator with a secret compartment in order to frighten people with the sudden appearance of what seems like a creepy child ghost.
Naturally, I do not believe in ghosts and would like to think that my immediate reaction would be that the unexpected appearance of a child in an enclosed place had to have a rational explanation. But I am pretty sure that I too would be pretty startled initially by something so unexpected. One can only imagine how terrified would be the reaction of those who think that ghosts, zombies, and the like are real.