Why do chicks that are your best friends flirt with you?

I mean like I wore this suit today and shes never reacted like this. I mean she was like making fun of me, but in a fun way kind of. And you could tell she liked how I looked. But I don't know if that means she has feelings for me now or what. I've known her for about 4 months and we haven't gone out or anything yet. And whats the best way to ask her to homecoming without making it akward for both us?Why do chicks that are your best friends flirt with you?
if yall are friends just ask her as a friend

kids hair

hair fallicle