C, E-flat and G go into a bar. The bartender says, "sorry, but we don't serve minors." So E-flat leaves, and C and G have an open fifth between them. After a few drinks, thefifth is diminished and G is out flat. F comes in and tries to augment the situation, but is not sharp enough. D comes in and heads for the bathroom saying, "Excuse me. I'll just be a second." Then A comes in, but the bartender is not convinced that this relative of C is not a minor. Then the bartender notices B-flat hiding at the end of the bar and says, "Get out! You're the seventh minor I've found in this bar tonight." E-Flat comes back the next night in a three-piece suit with nicely shined shoes. The bartender says, "you're looking sharp tonight. Come on in, this could be a major development." Sure enough, E-flat soon takes off his suit and everything else, and is au natural. Eventually C sobers up and realizes in horror that he's under a rest. C is brought to trial, found guilty of contributing to the diminution of a minor, and is sentenced to 10 years of D.S. without Coda at an upscale correctional facility!

Good one -- I guess there's no replies because nobody could top it.

I have one that's almost as good but I think it's too off-color.
I'll just give the punch line, and maybe y'all can google it to get the rest:
"Know it??? I WROTE it!!!!"

......and then of course there's the old standby......likewise I'll just give the punch line on this one too.
Actually no, the line I have to give is the one just before the punch line:

"So how did you wind up with this 1-foot-tall piano player?"