Generally used in restaurant or foodservice environments when a specific item is no longer available. For example, "86 baked haddock", or "the mussels have been 86'ed".
used as a verb, to "eighty-six" means to "ignore" or "get rid of". Suggested theories of the source of this usage include:
Possibly a reference to article 86 of the New York state liquor code which defines the circumstances in which a bar patron should be refused service or "86ed". Another theory has it that this is rhyming slang for "nix." Interestingly, this seems to be an American coinage, unusual for rhyming slang.
Others have suggested that this usage originated from the famous Delmonico's Restaurant in New York City, as item number 86 on their menu, their house steak, often ran out during the 19th century.
Another explanation is that Chumley's, a famous 1900s New York speakeasy, was located at 86 Bedford St. During Prohibition, an entrance through an interior adjoining courtyard was used, as it provided privacy and discretion for customers. As was a New York tradition, the cops were on the payroll of the bar and would give a ring to the bar that they were coming for a raid. The bartender would then give the command "86 everybody!", which meant that everyone should hightail it out the 86 Bedford entrance because the cops were coming in through the courtyard door.
The term came into popular use among soldiers and veterans to describe missing soldiers as 86'd. Rather than describe buddies missing in action, it was slang to describe the MIA as violating UCMJ Sub Chapter X Article 86.
Another explanation is the possibility of a simple variation of the slang term deep six, which has identical meaning, and is simply meant to describe the approximate depth of a grave.
Another possible origin is the public outdoor observatory on the 86th floor of the Empire State Building, the site of more than 30 suicides.