I’ve been thinking about fun ways to mess with people. and the first thing that came to mind was silly string. that evil can of projectile gunk. oooh so fun. so. fun things to shot, throw or drop on people.
Silly String, confetti, water! (swirt gun, bucket above the door, etc), paint balls, foam or Nerf toys. those a great.
EDIT: now that i think about it, a pottato cannon with water (somehow) packed in it would also be funny…er fun.