I couldn't find it using the twin/s or bully tag but there's this manga/manwha I read a while back about these twin bullies (boy and a girl) that torment other students (and teachers I think)

The boy is more docile and from what I read didn't do anything while the girl was a psychological tormentor.

Unfortunately I don't recall any other detail :/

Is it Perfect Classroom?

So it was a manwha! I thought it was a manga...

Grrr! Unreliable memory! Thanks so much Calstine!