I totally would and wouldn't mind if my S.O. did as well; I think it's cute.
^ To each his own.
The danger in brushing off things at a "smaller" level is that they have the potential to get out of hand and become "bigger" and more serious. Your coworker, is not someone that you'll see once in a blue moon. You'll see them every week and may even have to work closely with him or her. You may at first think of your object of lust only at work......and then eventually find yourself thinking about them after work....when you're at home with your spouse. Also, it's not professional. In the event that the flirtatious sentiments are mutual......it's one thing. But if they're not.........it can make the coworker feel uncomfortable and create awkwardness, which isn't good for the work place.
For those individuals who are able to keep their feelings in check......more power to them.