Only When He's Naughty
It started with my offering him a spanking in return for some rather childish, bratty things he did. It started as a joke, but he got very quiet and offered to bring my my hairbrush.
I've since learned that he had a sister and girlfriend growing up in the 70s who regularly spanked him for misdeeds and he's wanted me to do the same since we met a few years ago. He's always associated clothing of the sort that young women wore in the 70s (skirts and dresses) with authority.
He's also rather fond of being 'forced' to wear panties for his spankings. He says it helps him imagine he's a naughty child while I scold him and redden his bottom. There are occasions that he really does deserve a spanking though. He had some friends over for a Superbowl party and left the house in a shambles. I asked him how this was going to get cleaned up and he said "we'll get a maid". Rather than that, I got him a maid's uniform and that night, he had to put on the dress, apron, panties, stockings and high heel shoes before cleaning the living room. He didn't enjoy it but he did it - and I flipped up his skirt and pulled down his panties afterwards for a sound spanking.
Sometimes I think he misbehaves intentionally to be put over my knee. If he's a good boy, I let him wear panties.