I'm very much a boob guy and with everything you do with women its about how you do it.
I have noticed women do not mind at all when I'm looking at their chest. It's hard to explain but there's a respecting way of looking which makes them feel sexy and there's a disrespecting way of looking which will make them think you're a pig.
I will even make jokes about how big they are when women are dressed to show them off. And when they are hidden away I will ask why she would hide those gorgeous assets from the world.
It's direct and blunt but the ladies seem to like it.
If someone were to assume I dressed specifically to show off my breasts, not just because I liked the clothes and was comfortable wearing them, and took it a step further as to comment on how big my tits are and that I was showing them off... I'd smack the fucker in the mouth.
Likewise, if I were wearing something that covered them up, like I am now since I have a cold, feel like shit and despite the blazing sun, I'm freezing cold, and someone asked me why... I'd make it very clear that I didn't appreciate the unsolicited sexual attention, and maybe that's part of the reason for covering them up. I mean just look at what you think is acceptable when you don't cover them up!
Guys in general like to check out tits, we all know you do it and most of you show at least a little consideration for how it might make the person attached to them feel.
I personally find it quite endearing when I catch a guy looking and he turns away all shy about it and tries to hide that he was doing it. What I don't find endearing, or even slightly acceptable is guys who continue to do so after being caught, make comments and all but drool all over them.