Why did my friend tell me she is now obligated to tell other that I am a pervert that looks up girls skirts after this?

She found out that I know girls wear shorts under their skirts and then she told me she has to tell other girls that I am a pervert that looks up girls skirts and that she will do it. Why?
Why did my friend tell me she is now obligated to tell other that I am a pervert that looks up girls skirts after this?
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