Whether in a relationship or not, just about everyone engages in “work relationships” (assuming you don’t work with all dudes- or maybe you like that kind of thing). This practice is acceptable to a certain degree, except when it’s taken too far.
These are the bros that can’t keep their opinions to themselves’. Maybe they have a significant other, maybe they don’t. But they think they know the whole story and they really don’t. They get one half of it and then assume they know a lot about you.
Unless your girl works at a cool company where happy hours are actually a good idea with co-workers, then you probably never see them more than once or twice a year at company functions. So how is it that this guy knows more than you?
What’s worse? He might have some awkward work husband/work wife name. He might try to get a little handsy. He might say some inappropriate shit that weirds out the female. It could be a number of things. But nothing will keep him from being that guy.