It happens unexpectedly. A stranger's hand brushes across a part of your body it's not supposed to. I've a guy friend whose crotch area was touched or grabbed (can't remember which) by a homosexual. I think he was in such a state of shock that he wasn't able to react. Have you ever experienced something similar in nature? If you have, how did you react? If you haven't, how would you react?
Also, what is "chansing" in English? Is it "made a pass at"?