Green’s Dictionary of Slang

1. sticky.

1990

T. Winton Human Torpedo 88: ‘Geez, Lockie,’ Phillip said one night, wiping that goopy banana juice off his lip.

2. silly.

1959		I. & P. Opie Lore and Lang. of Schoolchildren (1977) 199: A person who is ‘wanting in the upper storey’ is [...] goofy or goopy.
1968		T. Wolfe Electric Kool-Aid Acid Test (1969) 276: Oh hell! There’s no way to talk about that without sounding goopy.
1979		E. Torres After Hours 174: I hadn’t meant to get goopy in front of her.
2003		J. Lethem Fortress of Solitude 429: A Valentine’s theme: goopy bulging hearts speared by feathered arrows.

3. (US) sentimental, tearful.

1979

E. Torres After Hours 172: ‘Why you cryin’, Gail?’ ‘Because you’re crying. Because the tears are running down your face.’ She held me tight. I hadn’t meant to get goopy in front of her.