When you're fucking a girl on the beach, you pull your dick out, dip it in the sand, and stick it back in the girl.
I gave that bitch with the fat ass a dirty seagull the other day.
2 more definitions
When a guy cums in a girls ass and she then stands above him and squeezes the jizz out of her ass onto the guys head.
My girl gave me a Dirty Seagull at the beach the other day.
The act of applying sand to one's penis, either through the use of glue or some other adhesive, and penetrating another person sexually, either via anal or vaginal intercourse.
After Susan forgot to pick the clothes from the dry cleaner, Martin gave her a Dirty Seagull.