Green’s Dictionary of Slang

faastie adj.

also fasty
[? Surinam Creole fiesti, nasty, or feisty adj. (1); but note SE fuss and thus faas v.]

1. (W.I., Jam.) rude, impertinent, impudent.

[WI](con. 1950s) M. Thelwell Harder They Come 50: But she did also faastie so that none of the man dem she see satisfy her.
[UK]N. Farki Countryman Karl Black 29: The conductress was still quarrelling. ‘Damn fasty shit-house!’.
[WI]L.E. Adams Jam. Patois 42: No bada fas’ wid mi! – Don’t meddle with me.

2. (UK black) unpleasant, distasteful.

personal correspondence 10 July: Some more stuff for your files. . . I heard ‘faystie’ used by kids in Stockwell in the sense of horrible.