The act of ejaculating on someones
dvd copy of either of the two
Scooby Doo Movies and then screaming
zoinks at the top of your lungs.
Shaggy was beating off a
nutt in the mystery machine right onto a dvd copy of
Scooby Doo 2 : Monsters Unleashed.
The rest of the gang could hear
zoinks being screamed from inside the house.
Therefor Shaggy was Zoinking.