Green’s Dictionary of Slang

dirtball n.

also dirtbomb, dirt merchant
[SE dirt + -ball sfx]

(US) a dirty or generally unpleasant person; a promiscuous young woman.

[US]V.C. Strasburger Rounding Third 21: Some dirtball is liable to come up and ask me [etc.] [HDAS].
[US]C. Hiaasen Skin Tight 110: Or does it look like some dirtball in a junker went nuts.
[US]D. Gaines Teenage Wasteland 99: While dirts (dirtbags, dirtballs, dirt merchants, dirtbombs) dress like they just walked out of 1968 — ‘freaks’ — they are wholly ‘today’s kids’.
[US]Hope College ‘Dict. of New Terms’ [Internet] dirtball n. A sexually promiscuous person. Used mostly by college-age girls when talking about other college-age girls.
[US]F.X. Toole Pound for Pound 122: Who’s this Sykes dirtball?