Ive seen Irish sessions hijacked bluegrass players as well. A guy with banjo sits down at an Irish session, when they stop playing plays a bluegrass tune while the other musicians watch, then they play an Irish set, followed by a bluegrass solo and on and on a few times then he gets up thanks them, and walks over to his buddy at the bar and snorts, "phuh they dont even know the'foggy mtn breakdown". It just takes common sense.

nothing wrong with obscure tunes, I do it all the time to introduce new tunes. ALthough my rule is if no one knows the tune and joins in (I just play it once through, sometimes 3x through, but rarely 3 sets of tunes 3x through as a solo. Do that often enough and people get pissed off.

but something to be said for sessions that are for established players, if youve been playing for years you dont want to sit through a bunch of beginners playing simple tunes, you want to play with better players, and that type of session is often advertised as an advanced session. Also theres nothing wrong with sitting back and listening for a while.

having said that I encourage sessions that are for beginners, people have to start somewhere.