The most humiliating outfits i could think of would be those that symbolize a stark difference between Her Lover's masculinity (the reason She finds him so sexy) and the cuckold's lack of same.
For instance, here's one that i believe fits that description:
When i see this picture, all i can think of is a sissy cuckold being called downstairs to meet her wife's lover, and i'm the cuckold. Diane's already selected what i'm to wear and laid it out on the bed for me. When they're ready, i'm called downstairs to meet Paul for the very first time, dressed like a little sissy girl.
Just another one of my dreams.