I really don't find Dean sexist. I honestly think he's just clueless.

John had a normal life before Mary died. He grew up with a mother, he dated, married, lived with his wife and had children. Sam at least lived with Jess for a couple of years.

All Dean knows about women he learned from movies and TV - which are hardly reliable source material.

He's rescued women, fought against women, had sex with women - but he's never had a conversation with a woman or spent any extended time with one.

To Dean, women are aliens who smell good.