The act of taking out someones door knob while there asleep with the lights off, so that you can then place your dick inside the hole where the doorknob once stood. Once the dick is in the hole you then proceed to knock on the door, in result some poor unsuspecting soul(probably one of your friends) comes to open the door, therefor having him grab hold of your dick, so that you can brag about it the next day.
One night, a group of friends decided to play a prank on young Dylan, by unscrewing his doorknob and shoving their dick in the hole, and then knocking. Little did poor Dylan know that he was about to get knobbed, and that nothing but a dick awaiting the grip of his hand. The friends all had a good laugh, and little Dylan was scarred for life.
When one places an item on their doorknob to let others know that coitus is going on within.
Tim knobbed the door so we should probably leave him alone.
Shagged, Nailed or had sex with someone
Ben: Hey Terry
Terry: How the fuck do you know my name?
Ben: Haha, You knobbed Row's sister!
Terry: (Pause)... Oh shit.
To have a male homosexual encounter
Mick: "I got knobbed by 3 policemen at the weekend"