Green’s Dictionary of Slang

fast adj.3

[faastie adj.]
(US/W.I.)

1. interfering, meddlesome.

[WI]cited in Cassidy & LePage Dict. Jam. Eng. (1980).

2. cheeky, rude, impertinent.

[WI]L. Bennett ‘Buy Somet’ing’ in Jam. Dialect Poems 6: Noh tink me fas’ mah but de way / How fe her head peel aff / She musa had a double dose / A enemy air-craf’.
[US]E. Bunker Mr Blue 371: He had one of the fastest mouths in the Department of Corrections, and it occasionally got him into trouble.