Let's say someone commits a prank, and accidentally it results in another's death.
If the death wouldn't have happened without the prank, the prankster is going to at least get hit with Manslaughter charges. If the prank wasn't potentially deadly and just random sh**t caused by the prank kills the dude (like cellophane on the toilet, piss splashes on floor, victim jumps to avoid piss, slips and whacks head on bathtub) you might get a slap on the wrist, but if the prank had any reasonable chance to harm (like walking up behind somebody on the edge of the grand canyon and doing the push/grab "saved your life HAHA!" thing), the prankster is going to be screwed, as he should be.
Self defense yo, you would need a super bleeding heart jury to convict somebody for that.
I love pranks, love watching other people get pranked, but I hate the "easy" stuff. Loud noises when somebody isn't expecting it isn't a prank and the victim isn't a pus (or whatever) because he/she jumped. Doing sh**t to sleeping person isn't funny (ok, it is, but not when it's violent). But the worst is the "mom/smaller sibling/aunt thinks she is alone so I'm going to put on this mask, grab a knife and go scare the sh**t out of her" kind of thing. Those dudes need a serious ass kicking. You put on a mask, grab a weapon and attempt to scare somebody, you deserve whatever hell comes to you and I doubt any jury would convict you. (and you will likely suffer plenty anyway, knowing you killed your son or nephew or whatever, even with a good excuse, is still going to weigh on you)