I'm scratching my head over this thread.
I'm all for a bit of good natured fun, but I really have to question the upbringing and morals of anyone who thinks it's fun to lift someones skirts for a wee peek. Such people place themselves on the same moral plane as street walkers. Women who do this should be roundly chastised, and men should be sent to the hospital.
I hate to sound prudish, but if you think it's fun, then I think you place yoursef on that same moral plane too.
No self respecting woman would EVER allow anyone, (particularly in public), to do such a thing unchallenged and neither should you.
And don't worry about what they may think of you for defending yourself. They have already demonstrated what they think of you.