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: Great personality, but she's got a head like a bashed crab.
n.1. a persons face that has as much appeal as a bashed crab.
2. a crab that has been bashed
=bash crab ; smashed crab ; hat full of assholes
i must have had the beer goggles on last night, i just dropped off this bashed crab of a bitch hey !