We're not talking about silly little harmless pranks like hiding their stapler in some jelly, we're talking Derren Brown mind games where you think that they're dead, you're dead or that they've woken up in the middle of a zombie apocalypse. It isn't until they start crying hysterically and calling their parents to see if they're alive or not that you should start to feel a little bit guilty. Come on, it was only a joke... You definitely crossed the line but you're sure that they'll see the funny side of things in a few years time. Hopefully, they'll have accepted your friend request by then once they've gotten over it.