Green’s Dictionary of Slang

shit adj.

[shit n.]

1. [1920s+] (orig. US) applied to any thing or person considered bad, obnoxious, unpleasant, inferior, worthless, e.g. a shit teacher.

2. [1960s] untidy, unkempt.

3. [1980s+] on the bad = good model, excellent, first-rate.

4. [2000s] (UK black) any.