No, it is "bad" to compliment a woman's breasts because they deal with it

Every waking moment of every hour of every day women know that somewhere across the street, across the room or blatantly right in front of them; someone is ogling at their breasts. Every day some greasy weirdo accosts them on the street or in a bar. Every day, all day, women get to deal with the debris caught in the sexually pseudo-gravitational orbit that seems to surround their enigmatic mams.

They are simply fed up.

Be different, compliment something else, try their eyes or their lips or even their hair. Failing that, be really different and say something nice about their personality, or, say nothing at all. If the only thing that you find appealing about them is their tits, the relationship probably isn't going to work out anyhow.

And remember, rule number one is: it's ok to look, just make sure you don't get caught.