the act of administering a rusty trombone
to a man who's just taken a dump; likely to occur after both parties come home from a long night of drinking and eating recklessly, possibly at Chili's; no amount of cautious wiping makes a muddy trombone acceptable -- at least not on the trombonist's part
Dude 1: Before I knew it, I was on the business end of a muddy trombone.
Dude 2: You mean, RUSTY trombone?
Dude 1: Naw, bro. Lemme put it this way: she wound up with corn in her teeth.