That time we show3d up on time as usual for sound check in prep for a thoroughly prepared acoustic set.... an influential member of the organisation coming into the rehearsal/sound check from behind us, bellowing "What the hell are YOU doing here!?!?" (As booking boss, I calmly and briefly replied with the facts and got band members back into the tune).
Then the first audience member arriving loudly launched into, "Why can't we get an organist in this place!" (Because your busted effing antique organ has been deemed unplayable by all the local professionals-- and everyone here is toxic, we all managed not to reply.)
But my favorite 'bad gig' experience turned out well.... arrived to find the building locked up tight upon our confirmed arrival time for setup/sound check. Luckily we had a plucky and tall, very thin guitar player with us that time, who quickly found the barely-open window to shinny thru, and who then let us in the front door. That was so funny that we didn't care when only 4 people came to the 'community-building' concert we'd been asked to play-- we just used it as a rehearsal, after welcoming the dude whose place we'd broken into, when he arrived with the other 3. ;-)