rules for thee and not for me

Regardless of whether it was the first to coin the phrase 86, the restaurant business in the 1930s was one of the main incubators for its usage and development. Believed to be slang for the word nix, it was initially used as a way of saying that the kitchen was out of something, as revealed in Walter Winchell’s 1933 newspaper column that featured a “glossary of soda-fountain lingo” used in restaurants during that time. It later evolved into a code that restaurants and bars used when they wanted to cut someone off, because they were either rude, broke, or drunk, as in “86 that chump at the end of the bar.”

Here, have an article with about a dozen different possible origins for the expression to 86 someone or something. Btw, none of them have to do with killing anyone.

Yep, 86 just means to throw it out. It's old garbage, no one wants that.

86 is kitchen lingo for removing (in practice, leaving out) something. like if the ticket is for a burger and it says 86 tomatoes you don't put tomatoes on that burger. as i read it, it means "remove the president", interpreting it as "kill the president" feels like a stretch either way.