Green’s Dictionary of Slang

(UK society) of an event or person, as much as of food or drink, sickening, likely to make one vomit.

1982		Barr & York Sloane Ranger Hbk 158: gucky adj. Makes you feel sick.
1987		Jones & Wilson Incomplete Education 97: [...] yards of cheap velvet, lots of thick, gucky paint, and the occasional pair of antlers.
2004		K. Maxwell They Wear What Under Their Kilts 38: Alec gave me a drenching gun [...] It looked pretty simple—the dose of the gucky drenching stuff was set automatically.