One thing that always gets me excited is public humiliation - or simply the prospect of being exposed in some humiliating situation in front of more than just female at the same time.
(Just to be clear, I don't like being humiliated or playing in front of men, it's a total turn-off).
When being humiliated in front of other women, the psychological and sexual impact of the erotic stimulation is exponentially more than humiliation in just a one-one-one scenario. I would say at least 10 times more powerful with each additional female present!
This is by far the biggest set of images I have, probably because I find public humiliation so stimulating. My advise to females in control is to use other women around you to intensify the impact of your authority and his humiliation.
Personally, I only feel this excitement around beautiful or attractive women. It's actually more of a turn-off for me if I'm humiliated in the presence of an unattractive women or a man, so I would hope that never happens. However, the opportunity to use attractive women around me to humiliate me is sooooo easy, especially since its easy to see who I find attractive as I have no problem pointing beautiful women out, even when I try to be discreet and not get caught staring at them. There are beautiful women everywhere, and so many would love to collaborate (spontaneously or planned) in an amusing situation of my public humiliation.