Rule #47. The second your hands are dirty or preoccupied, your nose will be itchy.

Rule #47. The second your hands are dirty or preoccupied, your nose will be itchy. 

This rule observes that when your hands are preoccupied or covered in filth such as semen, your nose will be unbearably itchy. In this situation you can either suffer the itch, or get semen on your face. Lose-Lose. This is interrelated to Rule #10. which states that the severity of the itch is directly proportional to the inability to reach it.