Crusty rudder

A "crusty rudder," not to be confused with a Dutch rudder, describes the sexual act of a male squatting on a female and farting with enough force to produce an audible sound and send tremors through the female's face. In most cases the female contracts conjunctivitis.

Pharmasist: "Kirsten, how may I help you?"
Kirsten: "I need antibiotics for my conjunctivitis."
Pharmasist: "Oh dear! How did this happen, again!?"
Kirsten: "You know how Chris likes those crusty rudder sessions..."