Not at a show but....
I've owned my Challey since 1983 - bought it my freshman year in college. I'd just spent my whole year's savings to get her painted and drove to the mall with a friend of mine. We parked about 50 spaces from any other car out on the edge of the parking lot. We're in the mall maybe an hour and come back and my car's still about 50 spaces away from every car except one. A brand new Mercedes is parked right beside her, literally within a foot of my car on the passenger side. There is a big dent in my door with paint chipped off and matching, freshly transferred paint is on the Mercedes.
My response to that discovery was the only truly juvenile, destructive thing I've ever knowingly done in my life. In hindsight I probably wouldn’t do it again, but at the time it seemed like the only proper response a broke teenager could give…. I keyed their brand new luxury car from fender to quarter while my friend popped off the hubcaps, which we drove over on the way out. Hopefully, the Mercedes owner was able to put cause and effect together when he came back to his ride and perhaps gained a little respect for other peoples property. Maybe not, but I sure felt better about giving the lesson.