I'm actually in this situation right now, where a song/guitar circle I go to includes one very nice fellow who cannot sing on pitch.....and sings the songs in totally different keys from what he's playing. It makes singing along and playing along difficult.....and occasionally he stops the song because nobody's jamming with him.

I've decided to stay silent.......because I don't think it's something he can change easily, and he really does enjoy singing and playing.

If there were some small 'tips' I could give him, I probably would. Or if he asked for feedback, then I'd probably need to be (politely) honest. But I don't want to discourage him.......and I really don't mind playing and singing with him most of the time.