How do you tell a bad bagpiper to stop playing?

[Jack Daw]

You cut me, man. You cut me deep.

Just kidding! I just had to take the jab.

Argh! Meet me at the Clan MacIntyre Assoc. tent or the scotch tasting at the Long's Peak Highland Games come September!

[Nighthawk]

Argh! Meet me at the Clan MacIntyre Assoc. tent or the scotch tasting at the Long's Peak Highland Games come September!

You got it! Look forward to it. Mmmm... Single malt...

It depends.
1.) If he is surronded by people with torches and pitch forks, pick up a stick and join in, if you must.
2.) If he is surrounded by people enjoying themselves, consider yourself an effete snob and move on.
3.) If he is all alone (most likely if he is bad enough to warrant any action on your part) offer some useful pointer to improve him.

I like it!

[Jack Daw]

You got it! Look forward to it. Mmmm... Single malt...

Have you done that scotch-tasting? It's 3 hours of fun.

[Abax]

Whatever you say or think, remember that it takes courage to play in front of others. Even accomplished musicians feel the twinge of difference between practicing in private and playing in public.

Abax (a musician a while back).