What is the meaning of Ratty?

Resembling or characteristic of a rat; ratlike.

Infested with rats.

1. In poor condition or repair.

   In poor condition or repair.

   Crazy, mad; ridiculous; slightly strange, eccentric; also (followed by about, on, or over), attracted to, infatuated with.

   Annoyed, bad-tempered, irritable.

   Synonym of knock down ginger (“prank of knocking on a front door and running away”).

   Source: wiktionary.org