Used to imply in a satirical manner that someone is "Jelly" (jealous).
It is often used in question form, see example.
Guy 1: Dude, your girlfriend
looks like crap today.
Guy 2: Breh, you ain't Smuckers. So why are you so jelly?
Guy 1: No for real she does.
Guy 2: AIN'T even Smuckers.