I feel there is good humiliating milage out of a girl that I dated, but since I tried to hide my sissy fetish I couldn't do much in the bedroom. For her to see me in a sissy outfit with "cummies" in my diaper, well it's safe to say that there isn't much more that could humiliate me to that extreme.
But I would love to hear some other ideas! Maybe there is another angle for another answer that is even more humiliating!