The brutal art of absolutely destroying a man's no-no zone with your shin at such speed and with such a tremendous force, you effectively castrate him.
Person one: Yo man, did you hear that Ethan just got shin bashed in the dick bag by Big Bully Bobby
Person Two: Holy fuck is he ok?
Ethan: *Limps over* AW SHIT MAN MAH BALLS! *Collapses dead on the ground*.
A physically ugly/unattractive person likened to the sometimes messy aftermath of cracking open the shell of a freshly cooked "muddie" (mud crab for the Un-Australianised).
Bob: So what's she like?
John: Greatpersonality, but she's got a head like a bashed crab.