Idk why some people hate Yui.
So far in the story it seems all she did was try and find a way to be able to be extroverted and talk to her seatmates to make friends.
It just so happened that they all turned out male and ended up misunderstanding her kindness and falling for her.
The only one she actually seems to try and tease is Yuuki.
Even the smart guy from before was just someone she asked for help with in studying since they were previously seatmates and he was smart.
That's pretty normal.
I mean the whole thing of her being a "seatmate killer" is the boys own interpretation, when we learned she just did her best to make friends thanks to her sisters advice.
She probably just got tired of boys because they kept misunderstanding on their own.
So she ended up just assuming everyone else would be the same, so she was shocked when Yuuki wasn't.
She tried teasing him and playing the game since that's what others assume, but when she noticed Yuuki really didn't care she stopped trying to play the role others labeled her as and tried to actually pursue her feelings.
Honestly she's not even a bad girl.
Some call her a thot, but thots are waaaaay worse than her, she's in that position because others labeled her as such out of their own fake image.