Green’s Dictionary of Slang

(W.I. Rasta) to be rude or impertinent, to meddle in somebody’s business, to be forward.

1983		V. Bloom ‘Name Shame’ in Touch Mi, Tell Mi 19: But people fas’ yuh know man [...] An’ dem come call mi fool.
1986		O. Senior ‘Ballad’ Summer Lightning 112: Is force-ripe woman this? What you want to fass in big people business for?
1994		M. Montague Dread Culture 41: Bwoy, yuh fass.