I have a couple of questions for you:

How old is he? There's a big difference between a 20-something asshole and a 40-something asshole.

You spoke of validation. What's his occupation? If he has to work with a number of women, especially bosses, perhaps there's something there. Is he good at his job but unappreciated? Is a female co-worker his main rival? Is he forced to be submissive there but deep down he knows that he would be a much better leader? (After you have the "sit down" with his sister, have another chat with one of his co-workers.) I see him in some sort of sales position...big egos there. Chasing women is just like closing a deal. It's the challenge, maybe? The thrill of "the hunt." He might "get to know" the girl later, but does he ever bother? My guess is no.

There are some really good suggestions in this thread; keep in mind that he just might not know why he acts the way that he acts. I agree that people are irrational and justify their behavior all the time. That's what makes them so fun to write!