Can a married person flirt?

I've been watching Nip/Tuk on Netflix and I have to say that I really like the show. I'm on season 5 and the last episode I watched got me thinking. If you are married and you have a friend at work that you flirt with, is that wrong? This same discussion came up on Cosmo radio (Sirius/XM radio) and the responses were all over the place. I will admit that I am married, if you didn't know, and I have had what you could call a "work wife." We both knew our place and there wasn't any emotions involved, but we went to lunch together, talked about work issues, politics, work gossip, etc. Once work was over, we didn't email, text or call each other. We would always look at the schedule to see if we were working together and if for some reason we were on different days, we were disappointed. We didn't do anything to change shifts, we just worked the days as scheduled. So I guess my opinion on this topic is if both parties understand the boundaries a little flirting is harmless. I am open to hearing other opinions. Feel free to let me know what you think.