One idea I'm kinda a fan of is that Mad Hatters have the ability to alter their bodily dimensions at will; it's not a spell or the result of a potion or something, you won't ever see them actually do it, and they won't ever acknowledge doing it, even if you outright ask them; it's just something they like to do on their own inscrutable whims.
> You're sitting down to tea with your Hatter wife. You go up to the bathroom and when you return your previously petite wife has breasts to put a holstaur to shame. She never acknowledges any change and doesn't know what you're talking about when you ask.
> The Hatter waitress at your favorite cafe normally has a small but well-shaped butt, one you've admired many times; out of the corner of your eye, however, she looks like she has an absolute massive dumptruck that wobbles and bounces with each step she takes.
> You go down to the beach to get a proper suntan and you see a Hatter get out of her usual outfit to wear proper swimware; she looks flat as a board at first, but in her swimsuit she's so utterly stacked that there's no way in hell that her normal clothes would ever be able to fit on her.