When a green booger is applied to the penis before oral sex begins.
Imagine you're getting head from a chunky fat chick. She drops to her knees, causing a thunderous, earthquake-like shimmy in your house as she hits the floor. You look her in the eyes, disgusted at yourself for your disgusting fat chick blow job habit. Sick.
Before she envelops your cock with her slovenly horse gullet, you cram your finger up your nose and pull out the filthiest booger in history. You slather it all over your cock and cry "give me a salty cabbage, baby!"
She complies. And cries a little afterwards.