In '87, someone brought in a
huge rubber penis that made the rounds... it showed up inside a piano (easily seen by 2 torch singers while singing), in a shoe box during the Chorus Line scene that was supposed to hold mics, even in one of the guys pants pockets, after a quick change where the choreography called for them putting their hands in their pockets.
Strangely enough, it resurfaced in '88, partially zipped into the fly of our flyman, who swung his hips around at the dancers who were facing offstage, stationary, during West Side Story's "There's a Place For Us" Lots of shoulder shaking that show, for sure.
I, myself, had need for some payback, and devised the perfect plan. During Hot Ice, a motorcycle was driven onstage for Leader of the Pack. And the driver had needed to be tought a lesson about messing with me. He had a super quick change just before that entrance, so there was no time to undo what I'd done. I had smeared hair gel on the grips. Had to make sure it wouldn't ruin his costume, but still feel slimey. The tech who prepped the bike was forewarned, and he in turn told the entire crew. I kept a straight face thru the quick change, and heard him yell "Ugh, gross, what is this?!?!" a moment before he HAD to be onstage. I popped onto the headset just in time to hear the lighting crew laughing at the look on his face. He came off and asked "What was that stuff? Probe?" and I still played dumb. All day, he never guessed it was me. I finally had to tell him.

Proud moment for me <wipes tear>