I would up the energy a bit and say "oh cool, how do you know eachother." then if he does know her neg her ..."how do you roll with this girl!" briefly chat with him, if it is her bf then at least you'll know, if not (or if your feeling super cocky lol) then do something like fuck marry kill with the girl, ignore the guy, and walk her away. if he doesn't know her then amog him, say something like, "wow, does that ever work?" then ask the girl "whats the most ridiculous pickup line you've ever heard" (i guess that frames it as if the guy is a chump trying a stupid pickup line
) anyway, the same situation happed to me recently. I was talking to a girl and a guy she knew literally grabbed her away from me. sometimes you can't really get a word in without it feeling really awkward. In that case I would open a set next to them and have more fun than they are, then reopen in 2mins. If you have a couple of girls on your arms, laughing with you you'll probably find that the hb looks over every few seconds and may even open you...besides, your more fun than her afc friend.
might work... let me know
Jax