My Funny Picture - What are some good senior pranks that don't vandalize and easy to clean up?

What are some good senior pranks that don't vandalize and easy to clean up?

we need a good prank to end the year off with, though it's a little early better start planning early. hah. anywho, we need some good ones.

Well, some seniors at our school went up to the roof with a swingset and a dummy to represent each of our principals, they put the swingset on the edge of the roof, and made the dummies sit on each swing, they were each holding a sign that said Grad 2010. It was pretty hilarious. Don't ask me how they got that swingset up there, nobody knows D: Also they stuck forks into the front lawn to say 'grad 2010', but unfortuatly they had to clean it up :V
What we did was hiding alarms set for during lessons in classrooms, and let off bunches of helium balloons in the school hall with rape alarms tied to the end. The rest was messier, like spraying 'class of '05' in shaving foam on all the walls, water bombs, ketchup bombs, fake tan bombs, flour bombs, and drawing a pen!s in weed killer on the lawn so it all died in that shape.
stick a condom and a picture of Michael Jackson in ever locker and in lube write "Just Beat It". That's what seniors did one year at our school. I still crack up thinking about it.
Post-its... EVERYWHERE MUAHAHAHAHAHHAHAa