>>13156
The fear is what gives it the punch though, the resulting freak out from a fake could be fun, but it wouldn't have anywhere near the same kick.
This is purely from a fictional perspective however. If you're talking about something real than an embarrassment or even pain approach seems like it would be better. Have it be a bucket of ice cold water above their head, something akin to a dunk tank, or the possibility of uncovering themselves.
Pain has a direct result is some what harder to make reality, melting wax or some kind of object dropping on their feet comes to mind. Some kind of electrical shock could work too, though I've no idea what you could use or even how to rig up such a thing off the top of my head.