Daddy, why do some men stare at ladies?

I was waiting for a bus when a man slowed down and started driving super slowly, leaning way out of the window, staring at me with what was presumably supposed to be a lustful expression but actually looked more like he planned to murder me. Not all that attractive, to be honest, sir. Anyhoo, I was all ready to snap the picture of his van when I saw it had his business name and phone number on it so I thought maybe I'd get into some legal trouble with it and didn't. Plus, the way he looked at me was really pretty scary and there was no-one around. A few days later I saw what was presumably his wife or partner driving the same van with kids in the back. So that's nice.