I've never been to one.
Tell a lie, once. A Sunday lunchtime jam-thingy with a couple of guys who I was sort of in a drummer-less band with, but not seriously. We'd jammed a bit.
It was terrible. Embarrassing. Singer/gtr player thought we'd just have a spot on our own. The three of us. Except maybe a drummer would join in.
So when there was a lull with the 'house band', as if they might have been thinking about having a break, we shuffled up towards the stage end of the room with our guitars on!
I think we did one of the singer's songs (his best one. It was actually really good. He said somebody else had recorded it and he was really mad about that. So I don't know if it was really his song or if he co-wrote it or something 🤷♀️). Anyway I got through that alright, as it was the main song we'd jammed, and it was pretty simple to play on the bass. I'd followed mostly what I was given on a demo. But it was catchy!
Then our 'band leader' started playing the chords to Start by The Jam. I thought ok... I know this one, it starts with the bass. So I should be playing by now. So I then started playing, and we went through a few bars without the singer singing - then before he did start singing, a couple of the 'house guitars' joined in. Playing what soon turned out to be Taxman. Which it turns out is a very different song! That 'we' didn't really know how to play. The singer was so freaked out he didn't try to sing either song. It was a really bad Start / Taxman instrumental stand-off. With no drummer.
Then a few more awkward minutes before 'we' left.
I say 'we' because I wasn't really in a band with the other two.