1.When anything is said, done, or revealed that causes any chance one might have had with a once-interested girl to fly out the window.
2. When a friend ruins your chances with a girl by hitting on her himself, and using his dick to knock your cock off course. Even if he is not successful, your opportunity for procreating will be dashed on the rocks of awkwardness.
Dick my own cock is acceptable.
Stacy: "Really, you run a dojo? How interesting. Where is it?"
Steve: "Uhh, my mom's garage."
Bystanders: "Ooh... man. He just dicked his own cock."
Bill: "Hey, Gary, tell Amy here about that one time you fucked your cousin!"
Amy: (silent vomiting and departure)
Gary: "Why do you always Dick my cock?