A Homosexual man that rides the knob/head of the penis to minimize penetration/painfulness during anal intercourse.
A anal retentive (tight assed) person that won't do a friend a small favour. The payout factor is that usually during sex the entire penis (shaft and knob) penetrates or is riden. This meaning suggests that via being a knob jockey and not a cock jockey that they are not giving the other party the satisfaction of riding the entire shaft rather than just the knob. Somewhat of a bastard.
Dude, I heard Rodney is a knob jockey.
Frances, fuck that man is so tight with is cash. Fucking knob jokcey.