“He swayed his hand over my stomach”

I was riding as the passenger on the back of a motorcycle with my friend. We stopped on red-light on a crowded street where people were crossing the street etc. There was this man who crossed the street and he swayed his hand over my stomach to my back and when I caught his eye he smiled and gave me a wink. I was in shock and I couldn’t say anything. I regretted that I stood still and wished I had confronted him earlier.