Add some bathroom pranks to your arsenal... watch this video tutorial to see how to prank someone in the bathroom.
Wait until somebody goes into the bathroom, or any other room that had a door directly across from it, and make sure the door they go in opens in, not out. Now simply tie the two door knobs together with a special knot and there's your prank. They'll go nuts trying to get out of the bathroom. Use this as inspiration for one of your April Fools Day pranks!