Green’s Dictionary of Slang

1. (US) pertaining to excrement, i.e. shitty adj.¹

1967		I. Rosenthal Sheeper 18: Don’t lay any of your poopy old aphorisms on me.
1976		P. Conroy Great Santini (1977) 367: Cigars smell nasty and poopy.
2015		J. Stahl OG Dad 129: Hey, somebody else has poopy pants!

2. in fig. use, unpleasant, irritating; i.e. euph. of shitty adj.¹ (3)

2015

S. King Finders Keepers (2016) 320: ‘How poopy is that?’ Holly asked noone in particular.