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.
12 step recovery jargon referring to someone new who talks about how great life is, now that they'resober. Usually meaning that the person is out of touch with reality.
The new guy seems pretty happy for a dude who has no job, no money and no family. He must be on a pink cloud.