Okay, so, it's flattering... But it would still drive me crazy!
I know a girl in my class who does the same thing - it depends on who she's friends with at the moment, but she'll completely copy that person. She did it badly though - whilst one of the girls just appeared in grey cotton sweatpants and queenie heels and a big baggy sweater borrowed from her boyfriend, it would look kinda cute, because that was just her style! But the copycat would try to get the same look by wearing blue sportpants, wedges and a sweater that was not big enough to be borrowed from a potential boyfriend, nor small enough to be properly fitted. She made a complete fool of herself.
I think it's a compliment when someone buys the same earrings after complimenting you on it or something like that, but complete copying is just psycho.