Sam: 'learning process', yes. But part of the learning process involves paying attention and absorbing clues. Another part involves what happens when you ignore a plainly and politely stated request.

People that aren't very good (and I've been one) are fine playing along on loud tunes or songs when they aren't likely to mess up other people, or they can play quietly. I don't know if it's possibly for a bodrahn to be that quiet, if it's the only instrument accompanying a singer.

Above all, learning on one's own requires the person to be able to figure out if they're doing something wrong, whether it's playing the wrong rhythm, wrong note or simply playing when they shouldn't. If the person is incapable of figuring that out, other people can help them (if they listen). If they can't gauge their own performance and they don't listen to others, chances are they're never going to learn anything.

Another idea: next time, tape the guy playing along with you and give it to him. What he can't hear when he's playing, he might hear when he's listening. Don't bet on it, though.