I'm not sure there's a clear & reliable way for rating or ranking musical "competance", but in the OP's hypothetical
...yes that would hack me off, and I would leave. Or I would demand that Mr. Idiot Guitar Player Who Doesn't Know What Dm Is leave.
I'm a tolerant guy who can often find fun in small pleasures. And sometimes that means playing music that is, for lack of a better word, simplistic. (Which is not the same thing as "simple".) I love getting together and playing with musicians who know how to improvise strict dodecaphony from nothing more than a serial matrix, or musicians who's idea of fun is sight-singing from a Karlheinz Stockhausen score. Or a George Crumb score. But I'm just as happy getting together and playing with musicians who can throw down a tight compelling rendition of "Good Golly Miss Molly". Or "Farmer In The Dell".
However, I draw the line at music that sucks. If you can't play whatever it is that you're trying to play well enough to not sound like a remedial bonehead, I'm not going to find a lot of personal satisfaction in that experience, and my time is better spent elsewhere.
Lets say you said, "Lets jam around in Dm.". And then it was evident, that say perhaps the guitarist, did not really know what Dm was. In fact all you got was, "Oh, I just play by ear." And then you realize he just ain't cuttin' it. Would that hack you off?
...yes that would hack me off, and I would leave. Or I would demand that Mr. Idiot Guitar Player Who Doesn't Know What Dm Is leave.
I'm a tolerant guy who can often find fun in small pleasures. And sometimes that means playing music that is, for lack of a better word, simplistic. (Which is not the same thing as "simple".) I love getting together and playing with musicians who know how to improvise strict dodecaphony from nothing more than a serial matrix, or musicians who's idea of fun is sight-singing from a Karlheinz Stockhausen score. Or a George Crumb score. But I'm just as happy getting together and playing with musicians who can throw down a tight compelling rendition of "Good Golly Miss Molly". Or "Farmer In The Dell".
However, I draw the line at music that sucks. If you can't play whatever it is that you're trying to play well enough to not sound like a remedial bonehead, I'm not going to find a lot of personal satisfaction in that experience, and my time is better spent elsewhere.