Lets hear'em. Everybody who has played out must have at least one great/terrible story to tell. Most of us have probably lived most of the Spinal Tap misadventures.
I'll start it off.
My band was playing a lot, usually once or twice a week and we had just recorded our first album in the drummers basement on an old 8track and released it on cassette. We sent them to all the record companies, and Capitol records seemed really interested. The A&R guy asked for the dates for our next couple of shows so we gave him a list for the three best venues and put him on the guest lists.
We made a pact that we wouldn't check the list so we wouldn't get nervous or anything when he showed up. Of course the drummer runs back the night he showed up yelling 'He's here! He's here!'
We were on 2nd that night (that was my favorite slot), there were two other bands. When it was our turn they dimmed the lights and we all walked out on stage, did a quick tuning check, and were ready to go. The singer yelled out the count - 'ONE TWO THREE!' and we kicked into our first song as intensely as we could. Halfway through the first verse I noticed there was no drum fill where there was supposed to be one. Then I realised there was no drummer. I looked back and saw him running towards the stage with a panicked look on his face. We tried to keep it going like it was intentional but it looked so stupid people were laughing at us.
We didn't get a record deal that night.
The other one that sticks out is the night we were headlining a big show with this band that had just been signed, so all the record people came out to see them and they stuck around to see us, which was really cool of them.
At the time I was playing my SG which I had to sell all my crappy guitars to pay for, so I didn't have a backup. We got on stage, drummer was there, everything was all tuned up. The song we opened with I used this wierd alternate tuning and it started off with me doing the intro by myself. First note I hit I broke the de-tuned g-string and I couldn't figure out how to wing it because of the ridiculous tuning I was using, so I had to stop and fix it.
By the end of the first song we cleared the joint.
I have a lot more, but those are my favorites.