Just an example of how bad something like this can go:
Once I played at a studio session for a demo tape for an acquaintance. The engineer liked my playing and said his band had a regular gig at a bar in Buckhead (sort of an upscale party area in Atlanta at the time- they've since tamed the party atmosphere in the area) and that their bassist wasn't going to be available for an upcoming show & invited me to fill in.
I asked for songlists, tapes, whatever. He put me off for a while but finally burned me a CD of songs to learn about a week before the gig. I worked my ass off learning those songs & making charts. Night of the show (I think we played from about 10pm to 1 am), they played ONE of the songs from that CD (Plush by STP). I think we played it in the 2nd or 3rd set.
The rest of the night they played jamband crap I'd never heard before. Granted, it may have been really popular jamband crap that they expected me to know, but as I am not from the jamband world, it was all just crap I'd never heard. Not only were they entirely playing material I was unfamiliar with, they seemed to be taking the fact that I was unprepared for this material personally. It was a fairly wide, shallow stage area. I was on one end, the singer/acoustic player in the center, and the guitarist (the only guy I had met) on the other end. So I wasn't able to see the guitarist's hands very well.
Whenever I tried to watch the singer/ acoustic player's hands to figure out what the f**k I was supposed to be playing, he'd either turn his back to me or immediately start vamping way up high on the neck so I couldn't distinguish the chords. This happened often enough that there was no way it wasn't on purpose. He also made fun of what I was wearing over the mic. All this in front of an absolutely packed house. This was the most humiliating night I've ever had in 40 years of playing. Horrible, horrible people.