A slang term used to describe the scum that accumulates around and under the foreskin of the penis as a direct result of excess masturbation. It, as the name might suggest, also reflects a generally dirty nature which is frowned upon by even the skankiest of bitches such as a Corinna.
Those most likely to 'Derek' as said to be from the state of Pennsylvania.
One might say "Dude, I've been jacking so much today I've started to Derek... Smells too".
To which the other person might vomit, turn their nose up or deny any knowledge of ever knowing that person because he Dereked.