We went, we sang, we got invited back for next week! Celebratory kittens all around! (This is the TeenChild's friend's kitten, who napped on me after we got home.)
There was only about a dozen people there, and, apparently, they could barely hear us at the other end of the bar, but the bar owner was there and she invited us to come back and sing again next week! This time, with a microphone and an amp. LoL. She said we sounded good, but the acoustics of this particular bar are pretty bad for an unplugged act.
It wasn't nearly as terrifying as I'd expected/feared. For which I am very, very glad. (The Rum Runner my buddy made me sure helped!)