Clearly I touched a nerve with my last post.
A few more contributions to the proper etiquette of sitting in on a jam session from bassist Carlo Petrovitch (someone who's seen it all...)
25. Don't call a tune that you don't actually have a clue how to play.
26. If you don't know a tune; don't suggest that you'll play it from ear when you actually cannot play by ear.
27. If you don't know a tune; don't suggest that you'll read the chart when you have no idea how to read or transpose music at sight.
28. When you get lost in the changes and eventually stop soloing 10 measures short, don't look at the bass player to some how fix your awkward silence.
29. After a bass solo, play the melody out. If you're not paying attention to the form and forget to come in; don't ask the bassist if they are done soloing 10 bars into the form when it's clear that they where finished 10 bars ago.
30. When playing a really really really fast tune don't ask the bass player to play a solo, they are to busy playing bass.
31. Having a conversion on the band stand during the bass solo isn't a good idea, especially if the leader is the bass player.
32. Call Jazz tunes at a Jazz Jam session, not pop, rock, r&b, rap, space age funk or any combination thereof and expect anyone to know them.
33. If you play a horn please do not accompany behind the bass solo. If you are in the rhythm section you don’t always have to play behind the bass solo.
34. When calling a really obscure tune and the rhythm section admits to not knowing the changes; don’t reply with “Really you don’t know that tune?” Beware, the tables can turn on you in a hurry.
And finally, a wise piece of advice from trumpeter Patrick Boyle directed to those who might feel inclined to adopt a "drop in/parachute" style of sitting in on a session:
"It is also the height of lame for a jammer to play a tune and then leave the venue right away. It is polite to hang out, even for a little while, to listen to a few other players and generally contribute to a good vibe of a jam session."