Magicmiles' thread asking for benign prank ideas got me thinking: What are the worst pranks you've seen, in person? Ones that cause serious psychological (but ideally not physical) trauma/terror/whatever to the intended victim? I'll start the ball rolling:
My ex-girlfriend's sister Victoria is seriously arachnophobic. It's easy to prank arachnophobic people, harder to do it creatively. Her boyfriend's buddy decided to have a go at it. He first got a Kinder Surprise egg, unwrapped it, and carefully split it open along the chocolate's seam, the part where the two halves meet and are fused. Emptying out the contents, he then obtained a really freaky-looking spider (must have caught it himself) and placed it in half of the chocolate egg. He closed the egg, spider inside, and fused the halves together again with a lighter, careful not to get the egg too hot. Finally he wrapped it and put it in the fridge, awaiting Victoria's return home from work.
She was stoked to get a Kinder Surprise egg, opening it enthusiastically.....the scream could be heard down the block. Rarely have I ever seen someone freak out that strongly. Had to laugh though. Had to.
What's one of yours?