Guy looks a woman over - normal - not sexual harassment.
Guys looks a woman over and makes a remark to her like, "Looking good today." - normal - not sexual harassment.
Guy looks a woman over and makes a rude remark to her or a bystander like - "Nice jugs." - not normal in a professional setting - he needs a talking to.
Guy stands in an elevator with his back facing the door to face a woman and looks her over the whole time without saying a word - not normal - kinda creepy - but I'd still have to know a little more to decide whether or not it's sexual harassment. Like, is there any polite interaction that ever takes place between the two of them, do they speak to one another, or is this the only sort of thing she can expect from him whenever they are in a room together? Does he act this way with all the attractive women in the office or just her? I ask that because if he does it to all of them, I'd consider him just rude, but if he's singling her out then it becomes more personal, intimidating, and uncomfortable. That might make me think that she should say something about it to someone.