You know how you fold socks one inside the other? To play a small prank on someone, fill ALL of their socks with confetti.
Make sure it is the outside sock,so that when they pull them apart the confetti will fly out and make a nice mess all over.Make sure you do all the socks.Put them all back in the drawer wihout leaving a trace anywhere.
or
You know those white security tabs that make the arches go off at the counters or the doors? Strip them,take the little metal piece out and stick it in peoples shoes ,coat linings,pockets,anything.Then take them shopping anywhere you want.They'll activate the alarm everytime and everywhere they go.Don't tell them it was you that did it,give it some time.