Here's an amusing practical joke to try: take a full pop can, unopened, and poke the tiniest pinhole you can in the side. Shake the can up vigorously with your thumb over the hole, and, while no one is watching, leave it at about face level somewhere where people walk past, with the hole facing out. A window ledge in a narrow hall or the top of a wall or fence is perfect. Everyone walking past will get hit by a tiny spray that's almost invisible but very disconcerting. You can even sit somewhere and watch discretely. :)