lol It's another word in a long list of insults for people who are ignorant in magick. Not new, not inexperienced...ignorant.
A fluffy/fluffy bunny/McWiccan/ect is a person who has read very little information on anything occult related and thinks themselves fully knowledgeable. They tend to be convinced there is one way to do something (which just so happens to be their way), anything and everything is possible and refuse to think outside their own little box of black and white.
The primary definition of a Fluffy Bunny is one who refuses to learn, refuses to think, and refuses to consider the possibility that they could possibly ever be wrong. Generally, they find one book, author or website and follow it as if it were the holy word, frequently denouncing anything that disagrees with it as obviously false. Fluffy Bunnies rarely get past the defense of "Because [insert favorite author here] says so." Sometimes they don't even get that far, responding to any and all criticism with something like, "You're just trying to persecute me!" - Catherine Noble-Beyer