In the movie the Matrix, one of the test that was given to Neo is for him to go on a walkabout in a controlled Matrix system, developed by one of his fellow freedom fighter. In that control environment, he was to be aware of his surrounding less any one of the Matrix agent will take advantage and catch him. As he was walking among uncaring pedestrian, a girl in a red dress walks by, he was distracted, and an agent made an appearance in front of him, he was caught and he failed the test.
Back to the real world where men and women live happily as couples, there is this normal occurance, which happen at least once in that couple's love life. While they are out dating, whether at a park, eating at a restaurant or walking down the road, the man is distracted by another woman. Whether it was due to the person's looks. The dress which may be a bit more revealing. Or just that the girl is considered sexy, which is subjective, to the guy's eyes. The guy will at least glance through his eyes, either a full eyeball's view or just using the skill of peripheral vision. No guy can resist watching another attractive girl pass him by without trying to steal a glance.
In my relationship, I am glad I have a wife who seems to be, not just allowing me to have a wandering eye, sometimes she is the one who spotted such girls or women and points it out to me. I know it maybe a bit weird and rare, and I know those who does that even endorse their husbands to do more than that (swingers group anyone?). Even when we were honeymooning in this island called Phi Phi Island where the beachcombers love to run around topless, she also kind of 'helped' me to ogle all those who have these exhibitionist traits. It is a thing which we had developed since we were dating and people watching especially in places of high traffic do become our favourites. And I know quite a few couple who does it together too....
If it's a model on a catwalk, I can ogle as much as I want