Green’s Dictionary of Slang

butt adj.

[butt n.1 (1a)]
(US)

1. (rap music) second-rate, inferior.

[US]L. Stavsky et al. A2Z.
[US]Hope College ‘Dict. of New Terms’ 🌐 butt adj. Bad or vile.

2. see butt-ugly under butt adv.