If I tell a guy that I have had a crush on him for awhile and he doesn't respond that he feels the same way, then I already know he isn't into me. If he further tells me to leave him alone, now I know that not only is he not into me, but he actively dislikes me (and possibly all women).
So, then, if he later approaches me and a gay male friend and the gay male friend says hi to the guy and he replies to the gay friend, my likely reaction is to pretend to be busy with my phone or get up and go to the restroom or at least look away and not acknowledge him, while probably also pondering whether he's actually gay and that's why he doesn't like me, doesn't want anything to do with me, yet has a cordial relationship with this gay guy to such an extent that the awkwardness of me sitting here doesn't stop him from coming over and saying "hi". ESPECIALLY if me and this gay friend have already discussed the fact that I hit on the dude and he told me to leave him alone, and gay friend replies that he also hit o this dude and this dude did NOT tell HIM to leave him alone. I would presume that I was disliked extensively by the guy, and would strongly consider that this guy was probably gay, hence his turning me down and telling me off in no uncertain terms while treating the gay guy's advances entirely differently.
Then again I'm an aspie female who constantly reads too much into things and always with negative results so I wouldn't necessarily consider what I say as accurate.
But my shortened answer is "It means she thinks you don't like her so she's avoiding you".
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( Living in Parentheses ) - female aspie, diagnosed at 42 ~
BAP: 132 aloof, 121 rigid, 84 pragmatic // Cambridge Face Memory Test: 62% // AQ: 39