i used to have a girlfriend who frequently looked over her shoulder and say "ooooh, i think i know him!!" and i hated it. however i always encouraged her to talk to him and even suggested they should go out. she never did and never mentioned him again.

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dont appear affected or insecure..just make a joke out of it like, "maybe,but im not into guys,you know!"blah!blah and shit..who cares?u dnt need to change your answer,its your reaction and feelings dude..

Respond:
"yeah, and you are stuck with ONLY me" in a relaxed, smiling, confident way. Like you know that you are "the shit" as well.
Unless your personality can not handle that

Dude you're a bit touchy if some chick is talking about some guy in a fucking movie. I have had chicks tell me they thought their co-worker was hot. I did not let it phase me. I never asked her "so have you talked to your co-worker today?" I especially never let her think I was jealous in any way (she wanted me to be jealous because she basically told me I was too aloof and uncaring). Regardless, I ended up in her bed whichever night I wanted -- on my terms. Now maybe this co-worker of hers could have "stolen" her from me. If that would have happened, oh well. I still got mine and would have walked away happy regardless.

All of this really depends on how well you know her. If it is someone you have only been on a couple of dates with, it might be a test (don't fall for it). If it is a chick you know well and have dated for months, it could just be that she simply trusts you and is not trying to put up any fronts (i.e. she is just treating you like she would a close friend, which is not a bad thing because you both can be yourselves.)

In any case, who cares? Some dude in a movie is no threat to you in any way.