Look, it doesn't matter what someone said before or after they sexualized someone in a professional context. Here's why: human beings are smart. They know that things people say matter. Thus, if you are commenting on someone's appearance or sexiness in a professional context, that must matter to you.
Why is that important? It serves to undermine the person it's said about. Rather than being judged on their work, or their connections, or what not - they are now being judged for their appearance. And that steals credibility they may have had in other, legitimate arenas.
It says, I like you because you're attractive, not because you deserve it.
("Oh, Nancy's not a good lawyer - everyone just thinks she's pretty." "Well Bob got that promotion because he's so good-looking. He didn't really deserve it." Etc.)
And yes, in some contexts, we expect to be more casual and colloquial. But if you're in a professional setting, unprofessional remarks do insidious harm to the subject.