Egg on a shelf is referring to someone looks like an egg on a shelf. Specifically Elizabeth McDermad. She is the where this saying came from as she looks like a fucking egg on a shelf.
Nevyn: Hey Elizabeth
Elizabeth: Yeah?
Nevyn: You look like a fucking egg on a shelf
Used in the 1970’s to mean weed, marajuana.
Hey Susan, I’ve got so eggs on the high shelf I’ll bring over.