I haven't ever heard the "rats in the attic" phrase and I would interpret it more as having his own problems/ dirty business rather than being crazy. Mostly words rather than phrases are used in reference to weird/crazy people 1. Cuckoo (sounds like kookoo) 2. Psycho 3. Weirdo he/she "has a couple of screws lose" "not right in the head" "Mad as hatter" "Lost his/her marbles" "stores open but nobody's shopping" Hope this helps