I'd go around and poke as many people as possible with a sharp needle, and have a heck of a laugh when they all simultaneously scream "OUCH!", and shortly after get all "Hivemind lolz :D" on them.
OR
I would go around and butter peoples faces. I think the reaction would be quite awesome, much like Dikarikas facedollarbillstapling. What if your face suddenly was covered in butter?
OR
Tickle the fuck out of as many people as possible, and watch in joy and hilarity as people suddenly collapse laughing.
OR
Something else involving many people and an awesome mass-reaction.