Can anyone tell me a FUNNY but LEGAL way to get someone back for doing something unjust to you>?

Throw balloons full of foul smelling liquid at them.

Fill their drawers with sand. We did this to a friend in college. He had sand in his shorts for months after.

Another one that is really funny but takes a long time is to cover every inch of all of their stuff in Post-It Notes. They will come off easily enough, but it is a great moment when the person walks in and sees their things covered in neon slips of paper. And you can still use the Post-It Notes after, so you don't waste any!

loosen the legs of their chair or wait til they start to sit down and when they sit down or start to pull the chair out from under them or the chair will fall with them in it

laxatives in the coffee or cake (I know someone put it already but it really is the best!)

bake them brownies but put those chocolate-flavored laxatives in them instead of chocolate chips

saran wrap their car. Funny every time.

Take a huge crap on thier doorstep!!!!!!!!!