Sexual harassment

I was just at a grocery store with my mom in line to buy some pretzels, when I noticed a group of guys were behind us in line. My mom dropped something out of her purse so I quickly picked it up. When I got back up, the man behind me grabbed my ass. When we were checking out, I turned around and the man was smugly smiling. When I got into my car I bawled my eyes out telling my mom. Maybe I’m just being dramatic, but has anyone else had a story like this? What would you have done?