“Someone stroked between my legs”

I walked out my house to go to work on a Friday morning 8:05am wearing jeans. Walked past someone going the other way. Next thing I know I feel someone stroke between my legs and up my arse and I turn around to see him picking up his phone and smirking at me. I didn’t respond but feel awful. What if he does it again, worse? I’m so angry but I feel helpless to do anything, and guilty because I’m upset about what in reality is the least of what some women experience.