A dirty cado is when a man withdraws his penis from his pants and has lint on or around the head of it. This is caused by the rubbing of his penis on his boxers or long johns. After exposing this, he then tries to get a blow job. After seeing his partners reaction, he then tries to pick the pieces off of his penis, while she picks them out of her mouth.
After feeling something funny in her mouth while giving a blow job, she realized she had gotten a dirty cado.