Crackfic

You've run across some crackfic (also known as crack-fic and crack!fic). It's weird. It actually... makes no sense. But it's well-written, and against all common sense you're enjoying it. It's fun. Fic that's based on some completely unbelievable premise and yet is so well written that it's just silly fun. And addictive, hence the name. (The name may also refer to speculation on the writer's state of mind during the composition of said fic. AKA "What was s/he ON and was it legal?")