javascript:document.body.contentEditable='true'; document.designMode='on'; void 0 Post that on the top of any website and edit it. Not only is it fun but can also be used to prank.(even though it's past april fools day )
Hahaha, yeah, that was pretty neat. I remembered when someone on a hacking IRC said that to me(well, everyone on the IRC that is), and told us that was a hack. It was an epic fail for him.
Anyways, this is the first javascript prank I learned: javascript:alert ('Virus Detected!'