It's a slang term. What I was surprised to learn is that it's not as old as I am. According to Merriam-Webster (http://www.merriam-webster.com/dictionary/eighty-six) the "first known use" was in 1959. I was two. I was probably 12 when I first realized it had a slang meaning.
According to several on-line dictionaries it originated in the restaurant industry where it meant "take off the menu," and could also mean "refuse service." The latter meaning, together with the time of its alleged origin, take my suspicions in directions I'd rather they not go.
It was also Maxwell Smart's agent number at C.O.N.T.R.O.L. By the time Get Smart debuted in 1965 it had been in slang use for 6 years. I'm sure I've heard Buck Henry say that's why they picked that number, but I haven't been able to find it through Google yet. I did learn that I got the name of the organization wrong. It should be 'CONTROL. "CONTROL" is not an acronym, but it is always shown in all capital letters as if it were.' -- http://en.wikipedia.org/wiki/Get_Smart
Anyway, I can retire in 86 days. But I'll probably eighty six my career before then.
And until then you kids GET OFF MY LAWN.
