86

Uncertain but most probably from soda jerk slang from the 1920s for 'all out', referring to an item on the menu not being available.

The earliest mention in print is from 1933. The OED suggests possible rhyming slang for nix. Another possibility is that it is rhyming slang for deep six.

Cassell's Dictionary of Slang claims that the term comes from the digging of a standard grave, which is 2.5 feet wide by 8 feet long by 6 feet deep.

Other, more elaborate theories include Delmonico's Restaurant in New York City, as item #86 on their menu, the famous Delmonico steak, is supposed to have run out often in the 19th century. Another theory is that this term came from the New York speakeasy Chumley’s, which was a hotspot in the 1920s. Chumley’s is hidden inside a West Village building which has two entrances: a well-set-back main entrance on Barrow Street and an obscure back-door exit on 86 Bedford Street. When police were sighted approaching the main entrance, the barkeeps supposedly yelled ‘86 it!’ to signal the patrons to hide the liquor and exit quickly through the back door. The term became standard in the service industry for ejecting someone by the 1940s.