Ban guitars! I used to sing my own songs unaccompanied - having written them that way - but unaccompanied singer/songwriters are much thinner on the ground than unaccompanied traddies.

If everyone's fed up with the guy, keep up the social pressure. He may not notice one or two people heading for the bar, but if five people left at once it'd be hard to ignore, and if fifty people a day... sorry, got sidetracked. If two or three of you want to tune up, go into an ostentatious huddle to do it. And so on.

If it's only you who's fed up with him, you'll just have to put up with it. There's a certain kind of 'protest' song I can't stand, that starts by saying "things we all approve of are good and things we all hate are bad", then says it over and over again in slightly different words for four verses (plus choruses). But friends of mine regularly sing them, to general appreciation, so I keep my gob shut. They'd probably describe the kind of song I like as saying "there was a girl, she met a boy, everybody died" over the length of 25 verses.