I don't have many hang-ups at sessions but I do feel uncomfortable when some showboat cuts right across the established flow or nature of the session.
I'll lend my guitar to people I know or I believe will treat it properly. Trouble is it tends to learn chords I don't know!
I was at a sing-a-round once when mine was the only guitar there and it ended going round the room. That I didn't mind too much, except it came back in a different tuning, (I'd been getting a drink at the time.) That DID annoy me, it was a twelve string!