It’s usually used in the context of a restaurant kitchen. Like if they run out of olives they would yell eighty-six olives. So don’t sell anything with olives without warning and don’t go looking for them.
To add, that’s the only context I’ve ever heard it used in when working in restaurants (to convey that we can’t sell or offer anymore of a thing). If someone order a lasagna with no olives, no one will say “lasagna, 86 olives”.
Worked in an italian restaurant for a few years. IIRC our lasagna generally had pork sausage, yellow squash, onions, bell peppers, black olives and a bunch of the usual cheeses. Probably had some other veggies too but it’s been a while since I worked there.
It was good lasagna.