Surely can't be just me and you?
I don't really count as a musician cos I'm not very good, but on the plus side I'm not shy and I'm a bit of a show off, so I don't mind being not very good in front of people.
I enjoy doing an impromptu turn. In general, people are very forgiving of amateurs who are prepared to stand up and have a go, and If I make a balls up it just adds to the fun.
I once went in to a pub in Ireland, everyone was standing with their back to the wall, all around the room except for one person who was standing in the middle of the floor singing. When he finished his song everyone applauded like mad and then he returned to his place at the wall and it was the turn of the next next person along.
The rule was, if you wanted to stay you had to take a turn. If you couldn't sing or play an instrument you could tell a joke, do a dance or recite some poetry, do anything as long as you did something.
Everyone, good or bad got the same thunderous applause. it was one of the best nights out I've ever had.