My ex-girlfriend's sister Victoria is seriously arachnophobic. It's easy to prank arachnophobic people, harder to do it creatively......the scream could be heard down the block. Rarely have I ever seen someone freak out that strongly. Had to laugh though. Had to.
Sorry Az, but no - I wouldn't be laughing at that at all. What the guy did was to work out what her biggest weakness and fear was, and to engineer a situation where she would unexpectedly experience it. That's not "prank", that's bullying, plain and simple. Taking delight in the pain and fear of others? Sorry, I'm with Traveller on that one.
Not a big fan of pranks anyway, but my rules for them to be funny and okay as opposed to mean and bullying are:
1) (I've mentioned this before): it should take, then return on the reveal (as opposed to give, then take on the reveal). So....."Your car has been towed - actually I just moved it over there" can be funny. "You won the lottery - actually, no you did not" is mean.
2) No permanent damage - that includes psychological. In the case Azd quotes, how happy do you feel that woman would be to eat a Kinder egg in future? When the prank is finished, everyone should be in the same state as they were before it started, and - importantly - feel as generally well disposed towards the prankster as they did beforehand.
Bottom line - if the prankee is liable to respond with a laugh and "gee, you got me there!" then its fine. If they are going to be crying, or shaking, and saying "how could you?" then it wasn't a prank, it was harassment.
Gosh I sound po-faced. But I'm currently dealing with a case as a Rep where a woman is off with long-term stress due to "pranks" being played on her in the office, none of which were as extreme as the spider in the egg.