Flirting with Duncan video right here:
www.youtube.com/watch He doesn't flirt back like Teagan does. There's also a link there to a video that shows a female mage flirt with Cullen, that templar in the origin. It's very obvious that he likes her, but then he runs away. xD I'm playing a male mage this time, and he was kind of... sarcastically mean to that guy.
Actually, a lot of the flirting in DA seems to take place during the origins, so it usually doesn't interfere with the mission. I can see how it would seem that way with Mass Effect though. Still, if Shepard can do side missions after she stole the Normandy and Saren is waiting patiently at Ilos, she should be able to flirt with turian NPCs. Lorik would have been a perfect opportunity, since he asked Shepard to sit down and have a drink with him.

For the record, I wouldn't make characters who are already in a romance flirt with other people. That's cheating! xD I mean, my MainShep had no romance in ME1, so she could have flirted with Lorik.