Unfortunately, that is typical of disorganized low level jams, it's pretty much "wankers night out". For some of these guys it is their only opportunity to get onstage and by God they're going to play every note they know before somebody yanks them off the bandstand! A little scouting beforehand is a good idea so you can avoid these situations. But lest some folks read this thread and think jams are all just a clusterf--k there ARE good ones where you will hear incredible players who are respectul of each other and actual music gets made. And if you're one of the guys who plays well with others it can even lead to gigs, I've hooked into a decent number of those from playing at jams.