I have a few takes on this question.
If it's asked for the reason of, "if those are fake, then I hold you in low esteem" then it bothers me.
If it's asked more along the lines of, "if those are fake, then you deliberately chose to be bigger/fuller/perkier, then rock on!" then I'm okay with that. Mostly because that's the sort of attitude I'd be having.
The one other situation I can think of is when it's someone trying to hone their skills and asking for validation. Even so, I can't imagine that would happen so much in real life as much as while reviewing images (pics, movies), unless it's between friends and not between the viewer and the woman being viewed.
That said, I can guarantee there are many here who are simply disgusted with fake boobs, no matter what. If she went under the knife, that's enough of a qualifier to add the woman to the 'discard' pile. It matters not how natural or fake they look. I guess that's alright if you're being choosy about pics and movies, but when it comes to meeting women, that seems to be a little self-limiting, unless the guy (or chick) in question meets new women as often as he (she) changes clothing, then he (she) can afford to be this choosy.