I'm surprised Ken hasn't posted this, since it's through him that I know if it. This is totally a music geek joke, and even then, it's an eye-roller, but still clever.
A C, an E-flat, and a G go into a bar. The bartender says, "Sorry, we don't serve minors." So the E-flat leaves, and the C and the G have an open fifth between them. After a few drinks, the fifth is diminished and the G is out flat.
An F comes in and tries to augment the situation, but is not sharp enough.
A D comes into the bar and heads straight for the bathroom saying, "Excuse me. I'll just be a second."
Then an A comes into the bar, but the bartender is not convinced that this relative of C is not a minor.
Then the bartender notices a B-flat hiding at the end of the bar and exclaims, "Get out now. You're the seventh minor I've found in this bar tonight."
The E-flat, not easily deflated, comes back to the bar the next night in a 3-piece suit with nicely shined shoes. The bartender (who used to have a nice corporate job until his company downsized) says, "You're looking sharp tonight, come on in! This could be a major development." This proves to be the case, as the E-flat takes off the suit, and everything else, and stands there au natural.
Eventually, the C sobers up, and realizes in horror that he's under a rest. The C is brought to trial, is found guilty of contributing to the diminution of a minor, and is sentenced to 10 years of DS without Coda at an upscale correctional facility. On appeal, however, the C is found innocent of any wrongdoing, even accidental, and that all accusations to the contrary are bassless.
The bartender decides, however, that since he's only had tenor so patrons, and the sopranout in the bathroom, everything has become altoo much treble; he needs a rest, and closes the bar.
"I wish I had documented more…" said nobody on their death bed, ever.