MadmanWithaWhistle wrote:
I'm curious, why is this annoying?
Bingo, there's
another annoying question.

Seriously ... In my experience playing Irish trad, the word "jam" in that context is a red flag that has only ever turned out to mean one thing. Namely: "I don't know the tunes and know nothing about the music or sessions. But I'll fake it by improvising and playing rock/blues/jazz/bluegrass/klezmer/salsa riffs, and not really worry if it actually sounds good or if you mind because, y'know, it's all about me."
Or course, I don't assume anything without first talking to a jammer; there's always hope. They could simply be unfamiliar with the lingo. But empirically speaking, I haven't been wrong yet.
Here's an actual conversation that took place about a month ago at the session I host, as verbatim as I can remember it.
He: Hi, I really love this music. Are you here every week?
Me: Hi, thanks! Yes, there's a session here every week.
He: I love your guitar playing. I'm from [City X] and I play guitar, too.
Me: Oh, that's great. There's a lot of good Irish music and sessions in [City X]. Do you play Irish trad?
He: No, I play rock. Can I bring my 12-string guitar next week and jam with you?
Me: Well ... Do you know the tunes and the music?
He: No. But I play in a rock band and have a really good ear. Can I bring my 12-string guitar next week and jam with you?
Me: Well, this isn't really a jam. Everyone here has spent years learning the tunes, including the accompanists. And we're not improvising like a jam.
He: So I can't bring my 12-string guitar next week and jam with you?
Me: No, probably not, especially a 12-string. But if you like, you can come and listen. I'll introduce you to everyone. And I can show you some techniques and point you to some great resources to get you started playing trad guitar.
He: Why are you being so mean? I'm a really good musician. I just want to jam with you.
Me: I know, but this session doesn't really work like that.
He: Goddam @#$%^&*!!! [Walks out in a huff.]
Quote:
A mandolin player that can beat out a decent backup line is always a welcome sight at our little gatherings.
I played with John Doyle at our local session last year. And yes, he can play lovely backup lines on guitar or mandolin. Or, for all I know, on bongos.