Sentence:  I knew about the English Civil War, Cavaliers (wrong but romantic) versus Roundheads (right but repulsive), but I didn't think that was what he was talking about. I shook my head. “It means our willies aren't circumcised,” he explained. "Are you a <WSD>cavalier</WSD> or a roundhead?” 
Meaning of the word marked with <WSD> tags:  A man or boy with an uncircumcised penis.