twice last weekend a girl approached me to say "do you know this guy?"

first time was at a gig and i'd gone to the bar. i came back to my group but they were gone, so i asked a cute girl who i'd seen in our vicinity "have you seen my friends? they were right there. one of them was a dude with a face and hair on top" but she shrugged me off.

later on some chode is trying his luck with her, and she turns to me to ask "are you with this guy?" i return a quizical look whilst doing the finger in the hole motion with my hands. again, she doesn't get it so i just give her a shake of the head. she turns back to dismiss the guy, who immediately gives me a high five [? i guess trying to save face?] and the night goes on.

another night i'm out with friends on the dance floor and my mates blonde target comes over to ask "do you know this guy?" "never seen him before" i reply, not wanting to ruin any frame he may have going on. [if she says i do i can then smile to say im kidding, we go way back, but she doesn't] she then says "he seems really cute and funny" and i pull a not bad face. i go and intro to my friend to discover his fake name and nationality, doing my best to keep a straight face. he later made out with her mate.

but my question is, what's going on in a girl's mind when they approach you with this?

the cute girl i think was using me to scare off unwanted attention, from his pov i could've been the bf. the blonde girl confused me tho, was she looking for me to qualify him, or bring me in to wing her female friends?

also, is there a universal winning answer? so far i'm thinking of "yeah" with a long winded monlogue about how we know each other with an ever increasingly asburd anecdote until blow out or i can get her to return to him and ask about the chilhood pet hamster tatoo done by his mother on his taint, purely for jokes.

obviously for mates i wanna wing as best i can, but otherwise i'm in it to win it. so how do i retort, for each scenario?