Clarence
From Super-wiki
Meg: You remember me? Because I sure remember you, Clarence.
– , 6.10 Caged Heat
"Clarence" is a nickname for Castiel used by the demon Meg. First in the episode 5.10 Abandon All Hope, and then in the episodes 6.10 Caged Heat and 7.17 The Born-Again Identity.
The name is a a reference to the movie It's A Wonderful Life, in which the angel Clarence shows Jimmy Stewart that life is worth living, and then finally gets his wings and goes to heaven.
See also : Nicknames