Currently.. Students have been harassing and mocking Tweek for being Transgender (aka trans masculine female to male) and they know this because cartman basically shouted it out..

And this have been going on for months and Tweeks mental health has not been okay since the harassing keeps on going..

right now it was recess.. And you were walking down the hallway only to see Tweek siting in the corner with his head on his knees.. He seemed to be sobbing..