Wind Up's. They can be highly amusing if done correctly. Some people make a career out of doing them. There's a radio station over here that does them reguarly in the mornings to good effect, shows like Punk'd pull off high level ones. I myself have instigated one or two in my time...a fact I'm sure Ross will testify to.
There is though a fine line between a humourous wind up and over stepping the mark into dangerous territory where the joke back fires and you just piss people off. That occurs when you take it too far. When you just cross the line thinking you'll be safe because your performing the wind up from a distance and you think no-one knows who you are. When you see the reaction and want to goad it some more. When you think you have the upper hand and you just push the button a wee bit harder and the witty remarks become insults instead.
To be able to carry off a good wind up, in particular when the person you are winding up is known to you quite well, you need to know when to call it a day. You need to have a bit of intelligence to read when enough is enough...to make a get away before you leave evidence behind that if looked at closely enough will reveal your cover.
For example if your wind up took the cover being done by written word (perhaps by passing yourself of as someone your not) then you have to look carefully at what you write because silly spelling mistakes and the words you use can all give clues to your identity, your age and your sex.
So to the little wind up merchant who has been trying his hardest to come the smart ass in recent times with me...
If I had to mark your report card it would need to read must try harder. I know who you are and I know that you know that I know who you are (did you follow that or was it too difficult for you?). So we'll leave it at that...never try to kid a kidder...espcially one more intelligent than you. Come back and try again when your old enough to vote!