Green’s Dictionary of Slang

1. viscous, sticky.

1996		P. Hensher Kitchen Venom 4: Nor were the pastes and thick soups, the inadequately complicated gloopy mixes to empty into dishes altogether the right sort of thing.
2000		Guardian 1 Jan. 14: The gloopy food that is delivered to my door once a month.

2. (also gloopie) stupid.

1965		I.C. Karp Doobie Doo 161: Now you’re getting gloopie and mean [HDAS].
2000		Indep. on Sun. Culture 7 May 4: She and the film throughout are gloopy, dreary, hammy, corny.
2023		R. Milward Man-Eating Typewriter 69: I regarded him with gloopy opals.