I've got a doozie.
Dead show, Tinley Park, IL 1990. Sitting in the lawn with a few friends.
Maybe 15 feet in front of us, a probably 40ish couple, kinda dumpy, sit on a blanket. Dude has his arm down the back of her pants like to the elbow. Before long, it's clear to us and others around us that he's mining heavily in Hershey Canyon (ew!).
Up the lawn walks an unsuspecting Head, a little wasted of course. He stumbles on them and their blanket a bit. Being obviously a nice guy, he stops to apologize to them. Dumpy guy sticks his hand out - THE SAME HAND THAT'S BEEN CONTAMINATED IN HER RUMP ROAST!! As the poor bastard reaches to shake this guy's stankhand, an audible groan rises from a bunch of witnesses, but we couldn't stop it in time. As he shakes the guy's hand, the groan turns into a gasp and exclamation of horror.
I'm pretty sure none of three of them realized what the commotion was about. As the victim continued up the hill, the best part was that some good Samaritan intercepted him and must have told him what happened. The look of abject disgust on his face as he looked at his hand was friggin' priceless!
Poor guy BOLTED towards the bathrooms afterwards, and a cherished story was born.