Green’s Dictionary of Slang

bad-ass n.

[SE bad + -ass sfx]

1. [1950s+] (US) an unpleasant, aggressive individual; thus superlative baddest ass n.

2. [1970s+] (US) on bad = good model, a tough, admirable individual; also occas. metonymic for one’s whole body.

3. [1970s+] (US black) an untrustworthy male.

In derivatives

badassery (n.)

[2000s+] the qualities implicit in sense 2.