What does 86 out mean?

Answer 1

I don't know if that is true everywhere, but in New York restaurants waiters and waitresses use this term to indicate that a dish is no longer served, especially when among patrons. They may say: VegiBurger 86, meaning kitchen ran out of VegiBurgers. I guess this is done to conceal such event from customers.

Correct - it's an NYC thing and here's why . Chumley's in the west village (currently closed)

was a speakeasy during prohibition. Right up until the day it closed ~ 2 yrs. ago, there was no signage. The 86 (for 86 bedford, it's address.) was the only marking. When a raid by the feds was suspected the NYPD would warn the staff to "86 everyone out"