berk (n.)

"fool," 1936, abbreviation of Berkshire Hunt (or Berkeley Hunt), rhyming slang for cunt but typically applied only to contemptible persons, not to the body part.

This is not an objective, anatomical term, neither does it imply coitus. It connects with that extension of meaning of the unprintable, a fool, or a person whom one does not like. ["Dictionary of Rhyming Slang," 1960]