I set my rig up earlier this evening and was called away on another errand. I got that done and came back to sound check after the PA arrived and was set up.
I didn't know I was plugged into the mixer. I couldn't hear/feel myself. The whole time I'm looking at my rig thinking "wheres the power"? We get done after a couple songs, I'm shaking my head trying to figure out what the problem is. While closing my rack case I see that they plugged into one of the power outputs from my power amp instead of the line out from my preamp.
No wonder it sounded like crap.
What kind of damage will this do to their mixer channel, amps, and speakers? Will it do anything to my equipment beyond siphoning watts from my speaker cabinets?
I wouldn't plug anything into someone's equipment without asking/showing them to confirm that its okay and avoid "total protonic reversal. That's bad. OK, all right, important safety tip. Thanks, Egon."
Sound check/set up idiocy 
