Do you have any suggestions for manga where the main heroine isn't scared of the fanclubs that see her as a threat (potential girlfriend of the boy they are fans of), and actually bets them\tells them to piss off?

well there's Koi dano Ai dano's Kanoko-chan who

is "best friends" with this popular guy, and she gets hate letters which she keeps as blackmail material

and maybe Ouji ga Watashi o Akiramenai! where

the main girl almost throws an vase at here bullies for ticking her off