Tech for this last show, I was mixing up a new batch of blood, and had dripped a little on my hand, to check the color against skin. As I was walking to the sink to wash it off, the ATD came down the hall, the other way. On a mad whim, I said, "Robert, you really need to fix some of those protruding screws backstage!" and held out my hand to him.
"Yeah, sure, where---- OH MY GOD!!!!!"
I wanted to keep the joke going, but couldn't keep a straight face. I was laughing for at least five seconds before he finally calmed down and figured out he'd been had. Then he chased me all the way to the bathroom and I had to lock myself in to avoid a beating.
It was a great laugh, and made my tech week. I didn't even plan it!