A penis that is skinny like a pencil.
Girl 1: Have you slept with Larry yet? Girl 2: No not yet. Girl 1: I heard he has a pencil cock. Girl 2: Oh great, that means he won't even touch the sides.
a pencil cock is when your cock is so thin its just like a pencil.
guy 1: hey so what's with you cock why does it look like a pencil?
guy 2: because i have a pencil cock.
guy 1: WHAT THE ACTUAL FUCK MAN WTF IS WRONG WITH YOU