I attended a gig at The Falkners Arms by a band called Mirrorball.
During the gig, a young lady asked the band if she could get up on stage and sing a song with them, to which they agreed. While the young lady was singing "Valerie" by Amy Winehouse, the lead singer stood by the table where I was sitting and put his glass on it. After a while, when he turned to pick up his glass, I attracted his attention and asked him "Can I have a go?" He asked me what I wanted to sing and I replied ""Sit down", by James".
He said that "Sit down" wasn't in their set-list, to which I replied "It's 8 beats in E, four in A and four in B. Rinse and repeat". He said that he'd ask the other band members during the break. Some time later, during the break, he returned and said that some of the band knew the song, so I would be up immediately after the break.
I was, too! I'm still buzzing! See also http://www.lemonrock.com/mirrorball?page=applause
Here's me at the Unicorn jam session on 15th April, doing backing vocals on "Mustang Sally".