"I tend not to sing songs when the composer is in the audience" wrote Paulo.

That's not a good rule to have - I love it when I hear someone sing one of my songs. Even if I don't necessarily like how they sing it, it's a great feeling. More especially perhaps when they've no idea you wrote it, because that way you know it's the song itself they like for itself, and that's what a song writer really wants to happen.

I suppose if you know the person who wrote a song is in the room, it might be a friendly thing to clear it with them, since there appear to be a few people who don't feel that way about their songs - and I suppose, if they were planning to sing it that night, they should have the first right to it. (Though myself, if someone asked me I'd always be happy to give over the song that night, and sing another.)