"I've been working out a lot the last few months. I managed to lose a lot of weight and I think I look good."
"Yeah, you looks great, that work definitely paid off."
The coworker brought it up, which indicates that they're comfortable talking about it and the comment is a celebration of the coworker's achievement rather than any kind of expression of sexual desire.
And then of course there are professions where the body is directly relevant to the work, like acting, modelling and sports/atheleticism.
All this really depends on context though. In a corporate office where everyone's barely more than strangers, I don't think even the situation above would be appropriate. In a small business where a "coworker" is as much a close friend as a colleague, I think the threshold for what's acceptable is very different.
Right. Its a comment on a thread, it has zero context. You don't know whether it was or wasn't appropriate based on the context.
You're jumping on the "unprofessional" bandwagon without investigating further. An "affirmative stance" if you will.
You don't see the irony?
This is why I avoid gender politics like the plague, the debates are not grounded in logic and rationality.
"Hey Googlette, you look really good in a bathing suit" is a comment about how the woman's body looks in a revealing outfit. I'd say this is generally unprofessional, though in some contexts (perhaps she'd just been expressing a lack of confidence in her body), it could still be appropriate.
"Hey Googlette, that bathing suit looks really good on you" is a comment on the particular bathing suit and how the combination works well. It's potentially more of a comment on her good choice and fashion sense than on her body. If the bathing suit is particularly risqué then it might be inappropriate but if it's just a normal bathing suit I don't think it'd be any more inappropriate than "your new haircut looks really good" or "is that a new top? It looks really good".