Green’s Dictionary of Slang

posey adj.

[SE pose]

(orig. US) pretentious.

[US]Eble Campus Sl. Apr. 7: posey – trying to appear sophisticated.
[Scot]I. Welsh Trainspotting 114: The posey cunt’s goat that green basebaw cap oan.
[UK]Indep. Rev. 20 Apr. 1: He loves posy, pretentious film and sound effects.