Green’s Dictionary of Slang

-assed sfx

[ass n. (2)]

1. [20C+] (orig. US) describing someone’s ass n. (2), e.g. narrow-assed adj.

2. [1950s+] (orig. US) a general intensifier, e.g. panty-assed adj. [ext. of -ass sfx but note earlier half-assed adj. (1)].