Ha, my first gig was only 4-5 yrs ago.
I'd been working with a group who wrote originals and after a few weeks of rehearsing together, the BL booked a gig at a small, local festival. There were about 8 bands there, total, and we were second-to-last to perform. I knew the music, but didn't know etiquette at all. I was twisting EQ knobs on the huge amp sitting on top of an Ampeg 8x10 that was probably loaned to the venue by a real bass player lol. Didn't know that was a no-no at the time.
Got through our 3-song set well, and a few people actually liked our sound (THAT was really cool).
...BUT THEN....
The BL, for some odd reason, decided we should play the first song of the set... a second time (

?). I protested for a millisecond, but they insisted and counted us in. The second time around, it was a
DISASTER 
. Somehow, the drummer got off beat for a sec which caused the BL's strum (acoustic guitar) to become erratic and all over the place. I was trying to re-capture the drummers beat/tempo, myself (ANY beat lol), but failing miserably. I tried to reign the drummer back in with my limited knowledge of how to do so, but after a good 10 seconds of "what the

", we just couldn't seem to get on the same beat and the whole ensemble disintegrated into a full on train wreck. It was pretty embarrassing, but we just kinda plowed through the failure. Smiled for the most-likely disingenuous applause and got out of there lol.
Why the BL insisted on playing the same song again, I'll never know...
Still a fun/educational experience, though
