You can only get them from chests. They are roughly a 1% drop so good luck!
What makes them unusual?
Firstly, they will have a name like this. Unusual Honey Badger
Secondly, they come in the following particle effects
Affliction of Vermin
If you are still feeling lucky watch the following videos!
Edited by BanKon, 17 August 2012 - 09:42 AM.