This is a tough one Magnus, I did have a friend lift the back of my kilt in the bar one night, but we're old school buddy's and have been pulling all kinds of stuff on each other so it wasn't that big of a surprise to me. I've never had a woman lift the front of my kilts, more often than not I get somebody rubbing their hands on my legs, than a kilt lift.
Personally Iwould have a talk with the "good buddy" and proceed from ther.

Rob