The Amtrak (up thru the 1980s) passed right through our village
about 10pm every night and again at about 4 am. My friends and I used to stand a few feet from the tracks and moon them and/or flip them off and/or show our sunny sides. The passengers would have a look of momentary shock and they would then keep turning their faces towards us as the train continued on.
Go into Kroger (or Meijer or Walmart, etc.) and walk around and randomly (and covertly) put maxi pads and/or condoms into people's carts and then blend yourself into the scenery and watch their reactions. It's hilarious.
One summer at Ohio U, I was on the paint crew. We switched the telephones around from room to room and floor to floor in every dorm we were in, therefore no room had the correct phone number to correspond with what was printed on the phone. We thought we were slick. We found out at the end of the summer that we were not to only ones to ever think of doing that; it happened every year and the residence life and housekeeping staffs already had a plan in place to remedy the situation.