The first windmill said to the second, "What's your favorite type of music?"
The second windmill said, "I'm a big metal fan!"
Alright, listen up, you smooth-brain! This joke is playing on words, you see? One windmill asks the other what kind of music it likes, and the other says it's a "metal fan." Now, 'metal' is a type of music, but windmills have 'fans' that are made of metal! Get it? You probably don't. Did you know that you forget 90% of what you learn in school within a month? Also, I bet that when you get a paper cut, you ask for a bandage instead of just licking it.