Why is Bush called "Bunnypants"?

I notice that a number of bloggers who disdain Pres Bush refer to him as “Bunnypants.” I was wondering the derivation of the insult and tried a Google search, but couldn’t find anything other than some speculation concerning the cartoon character Crusader Rabbit, and how Bush hid out in bunkers just after the 9-11 attacks. These guesses weren’t very satisfying. Does anyone have a good idea where the nickname comes from?