When I was in the RAF, in the days when Pontius was a pilot, I used to play all sorts of tricks on people, examples being:
a) changing the contents of the blokes next door's shower gel to Deep Heat (there was a lot of screaming).
b) there was another bloke who used to cut himself every time he shaved, but kept putting on a brave face when he splashed Old Spice on it in front of us - until I changed the Old Spice to a salt and vinegar solution.
c) crouched down behind a tall bully, reached between his legs gently and pinched a woman's bottom. The slap could be heard across the room, and he just stood there speechless (enough time for me to scarper - otherwise I don't think I'd be writing this now!)
Oh . . . those were the days of frivolous fun!