When receiving oral sex from a kneeling patron, one covertly slicks the patron's hair back with their own feces much the way one would apply a cheap mousse. Thus, making them a shittin' image of a "muddy otter."
"I had to shave my head once that son of bitch gave me a muddy otter!"
Whilst receiving oral, one reaches back and shits in his own hand, then proceeds to slick his partner's hair with the poo, as though offering encouragement.
I decided to make my birthday blowjob extra special by giving her something in return. She loves a good muddy otter.