let the door hit you where the good Lord split you

Etymology
Described as early as 1977 as Black American slang constituting a "nasty command to leave, euphemism of 'split you' avoiding profanity." The phrase "where the good Lord split you" describes the crease of the buttocks.

Usage notes
Sometimes phrased as "let the doorknob hit you where the good Lord split you"; or as "don't let the door hit you where the good Lord split you" (implying that the person should leave, but avoid being hit by the doorknob on the way out) or even as "let the doorknob hit you where the dog should've bit you".