I disagree with all these guys. You don't have to listen to me, but it seems to me that just ignoring the boyfriend as if he was never mentioned is very AFC. What I always find works wonders for me is treating the boyfriend like a welcome addition to the conversation. Ask the girl about him and if she mentions anything good then be as happy as she is. Mention how they make a good couple. But make sure you overplay him a bit. Make it seem like he's better than he actually is, which is something that she'll take note of. But NEVER compare him to you in any respect.
I could go into so much detail about why thus works and all the techniques it utilises, but just try it. As a matter if fact I used this today on the bus and was getting some major IOIs.
I figure an AFC just ignores the boyfried, whichnis just gonna get you lands in the fried zone. A mega AFC pretends like it doesn bother him but tries to talk the bf down. An alpha male takes it straight on but doesn't let it bother him. Good for her if she has a boyfriend! Because as an alpha male you KNOW your better than him.