Feet are pretty disgusting to me. I might kiss a girl's feet during mish if I was sure enough that they were clean, and definitely not the bottoms!
Kayla, I think the urge may strike due to simple proximity. The tops of the feet are actually pretty sensitive, too, which is kind of odd. Like the back of the hand and fingers....you can still kind of "feel" things.
I have, however, avoided that type of contact for the exact reasons you suggest. So sorry to hear about it happening to you, but that post was funny as hell!!