Looking at someone's chest can be offensive.
Dave's coworker, who has large breasts, starts talking to him about something work related.
Dave wants to look at his coworker as they are talking to him.
Dave looks his coworker in the eyes in a normal manner while they are talking to him.
Dave looks down at his coworker's chest for most of the time they are talking to him.
Dave's coworker sees Dave as a normal decent person and feels comfortable around him.
Dave's coworker thinks he is some kind of creep for just staring at her breasts while she was talking to him.