rđav

1. bad; poor
   Imali smo rđavo vreme celog odmora. — We had bad weather the whole holiday.
   To je bila rđava odluka. — That was a bad decision.
2. (of a person, deed) bad; wicked
   Ima rđavo društvo i zato stalno upada u nevolje. — He keeps bad company, so he's always getting into trouble.
   On nije rđav čovek, samo je tvrdoglav. — He's not a bad man, just stubborn.
3. rusty
   Na kapiji visi rđav katanac. — A rusty padlock hangs on the gate.

For "rusty", zarđao is the usual word.