ketchup bottle

Verb. Refers the action slapping the thumb-side of one's clenched fist into the open palm of one's other hand, mimicking the action of attempting to extract ketchup that is stuck within a glass bottle. This action produces a slapping sound that is meant to imitate the sound produced by the contact of flesh between two people committing vigorous sexual intercourse or similar act. In more rare cases it can refer to solo masturbation.