1. A dry, rough crust which forms over a cut or wound on the anus during healing.
2. An obnoxious, rotten, ungrateful, slimy and rotten-to-the-core person, of whom these characteristics are beyond that of an asshole.
Quite how I was wounded on my anus, doctor, I'm afraid I'm not at liberty to reveal, but you will note there has now formed on it an admirable rimscab.
That guy operating his convertible roof at the traffic lights looks like a right rimscab.