My long-time music partner, Tommy Johnston, was a small town judge, blacksmith, "killer" B-3 player and general "badass" when he wanted to be. He was about twice my age when we played together.

When asked if someone could sit in, he would have them get their instrument. If it was a solid body guitar, he would roll his eyes, assist with the tuning of the instrument, and then call out tunes like "Four", "Angel Eyes", "Wave" and others. Of course, the person knew none of them (usually).

Then, Tommy would say," Tell you what. Take that piece of SH** guitar home and don't come back and waste my time until you learn how to play it."

Funny, but no-one EVER came back. That's pretty rough, but he liked the key of E even less than I do! (LOL)!

The point is, jam session players, at least in a jazz setting, have to realize that "sit in's" have to be able to keep up, don't call tunes unless asked and, above all, respect the integrity of the music and the leader(s).

That being said, some of my fondest memories are of some "sit-in's" who "kicked ass" on the bandstand. Lou Rawls was one of them. I had a house job at the Campbell House in Lexington. He came there with his daughters frequently to shop for show horses and to get riding lessons for the kids.
He would simply look at me; I'd nod, he'd take my mike and proceed to blow me totally away, finishing the tune I was into...no fanfare...no introduction; just raw, delightful talent.

That's a "sit-in" I will forever appreciate....a great father, true gentleman and the reason I'm not a professional vocalist (LOL)!

Russ