Green’s Dictionary of Slang

gaggy adj.

[SE gag, to choke, to vomit]

(US gay) sordid, highly distasteful.

[US] (ref. to mid-1960s) B. Rodgers Queens’ Vernacular 92: gaggy (kwn LV, mid ’60s, fr pros sI) 1. sordid, unsavory, in the worst possible taste [...] 2. filthy, revolting [...] 3. (rare) boring, dull, square.