Pronounced: gaaat-fall. Meaning: very fed-up or irritated.
It is a South African word, derived from the Afrikaans language, but widely used in English (and some indigenous langue conversation.)
Literal translation: gat(ass or hole) vol(full)
Probably intended to mean a dug hole full to the brim (“up to your neck with…”) , but given a slant by the double meaning of the word “gat”.

A casual invitation / threat used by an individual that is not afraid of fucking someone up.