similar to the facehugger from Alien and the Headcrab from halflife, the asscrab kills you after it used your body, but the asscrab attacks your ass instead of the head

v. collectively or individually finding someone/something to blame for a problem, as opposed to brainstorming which connotes finding solutions to a problem

n. the act of finding someone/something to blame for a problem

(from a TV ad for HD television)

Persistant crabs that manage to burrow inside the anus.

crabs on your ass!

Haveing pubic lice on your butt and in the hair

n.) Generally used for a person or thing who, apart from being a complete asshole, is also very obviously crabby.

A small species of crustacean that resides in the anal region of male humans.
It feeds primarily on semen and unborn babies.

Best way to counter is with the head of a penis - their one weakness.