why men do this to us?

I don't know where to share this, i just want to get it off my chest. 10 hours ago a man passed by but came back and stop in front of the store where I work. He just stood there and stared at me, i didn't mind him and scrolled through my phone. But then he started playing with his private part while still looking at me. All I can do is go at the back of the store to hide. He didn't leave for 3 hours. I can't leave the store bc it's my job and can and there's only old woman sleeping near me.
I feel so dirty.
Why do men do this.