It is absolutely common restaurant lingo. I can use it with anyone I know from restaurants seamlessly.
That said, fast food work is a different subculture.
But wouldn’t the common restaurant lingo be “86 THE cherries?”
86 is a verb. To 86 something is to exclude it. But 86 alone is a number like any other. Just as 50 alone isn’t pronounced “five-oh” and doesn’t mean the Hawaii State Police. If I said “I’m 50,” you’d assume it’s my age, not my profession.
If I said, “That’s the shit!” I’d mean the opposite of “That’s shit!”
Mileage varies. I’ve seen “86 [thing]” written on whiteboards more often than not, grammatically speaking.
Also, a single cherry is the norm, perched decoratively atop the whipped cream. So “86 the cherry” would have been clear, and they could maybe get away with “86 cherry” according to you, but “86 cherries” might as well be “69 cherries.” You wouldn’t expect that to mean mutual oral sex.
Yeah, I’ve never once heard it when I worked fast food, only full service