Have a few stories, mainly in my originals days.
I remember a venue saying they would supply the backline for us 'so just bring your guitars'. Got to the venue and... nothing! Landlady asked us to make a 40 mile round trip to 'fetch our drum kit'. Announced we were going one way only and promptly left.
One of my first bands, in front of roughly 150 people, guitarist started the set without checking in first. I was still plugging in and tuning up yet he had already started the song... asked after the gig why the bass wasn't in the first song.
Same band, played a different venue and we were received well. Got shouts from the crowd for an encore. Singer announced I don't feel like it and walked off the stage.
Ah, a good one - had a lesbian couple make out to one of our songs during the set.
Best story is for various reasons, a venue at the last minute said our band could not play the gig anymore. When I say last minute we had arrived with the gear to load in. Not a clever move on their part - we were providing backline for a 5 band bill and 2 of the other bands were friendly with ours. Once they found out we weren't playing, they pulled out and the 3 of us arranged a gig, that night at a venue less than 100m away from the original venue. So no backline and only 2 bands remaining on the bill. The promoter was not a happy bunny!