The act of defecating into the pillow sheet of another person, due to extreme aggression, hostility, rage, or an attempt at a very funny practical joke.
Similar to the dirty sanchez, while doggy style, sticking your pinky into the girls ass then reach around and poke her in the mouth. The point is to leave some brown on her front teeth.
Heard it on the daily show, and decided to come up with a definition for it. A dirty toothbrush is when a man has anal sex with his partner and then takes his penis and rubs it on his partners teeth.