I can't claim to be a great singer, but I think I do OK. I try to pick songs that have meaningful lyrics and sing them clearly. I also play guitar, and supply my own accompaniment.

But if I put down my own guitar to sing un-accompanied, nobody else should join in unless I ASK them to. And I only do that with a few people who are top-notch guitarists.

I have no problem with giving a withering look, or holding up my hand. If that doesn't work, I'll escalate to "stop it" if need be.

Sometimes it's hard to get a song started in a session, because others aren't always paying attention to the other side of the circle. If I feel support from the rest of the group, I'll continue.