A polite, abbreviated version of the interjection "Fucking Ace." Calling something "ace" or "A" means it is the best, top or most extreme. Adding "fucking" lends emphasis. Can be used as an adjective.
a curse refering to the mammal known as an aardvark.
history:
back in the day, people would go rabbit hunting and they would see stuff movin in the field and shoot it. But then upon inspection of their quarry, it'd just be an aardvark
and they'd be like, "fuckin aardvark."