You can't put rules on a real jam night. If it's open door then they all get the 2 songs they've chosen and even get a second stint if there are not enough players to fill out the evening.
We had a guy who turned up for a couple of years playing Hendrix. In the end no one would play with him so me, as the house bassist, got lumbered. He was extraordinarily loud, had no timing to speak of and didn't play any of the chord changes in the right places. We was told to turn down a few times but never told he couldn't get up.
Thankfully there are usually enough good guys to balance out the idiots.