Anya hates bunnies. In "Once More With Feeling" she sings what might be my favorite lyrics of all time:
Bunnies aren't just cute like everybody supposes,
They got them hoppy legs and twitchy little noses.
And what's with all the carrots?
What do they need such good eyesight for anyway?
This is not the first expression of her fear of bunnies, nor is it the last. Wikipedia chronicles all of the encounters with bunnies she has in canon TV episodes, but it doesn't address the cause of the phobia. I believe it is never revealed in the TV show. It's one of those little Joss-isms, an inside joke that's never really explained.
So, the question is: do any of the canon comics (or novels or games or any other applicable medium) ever explain why Anya hates bunnies so much? Are there any hints we can glean from sources outside the TV episodes?