Usually in the form of "that's on Sundays," refers to a suggested activity which is rebuffed, as with movies which seem to play every Sunday on television.
Polio: "Why don't we rent Falling Down?"
Edwardo: "Nah, man...that's on Sundays"
Polio: "Why don't we go to the petting zoo?"
Edwardo: "Shiii...Sundays, motha fucka, Sundays..."