Being spat on and being forced to worship feet.
I didn't think I would like being spat on, and when my mistress originally spat on me I thought it was gross, but after the session I started to appreciate how humiliating that felt.
And I've only been told to worship feet once. I've never felt a disgust for feet or anything, I just felt nothing and never understood the fetish. But for some reason I got really aroused when a mistress had me lay down and shoved her bare feet on my face and made me kiss and smell them, it was unexpected as hell for me.