gesugao
An expression where a character is shown with a condescending, menacing, and sinister look. Often shown with an evil smile, smirk, or sneer, giving them a sense of sheer disdain or superiority towards the viewer or other characters.
Usually used with a normal/nice character, to show an out of character moment. But can also applied to a character who canonically has such a face or using it to emphasize their evil side (particularity when said character is betraying the protagonist), so that the viewer would feel a sense of satisfaction when these character were defeated.
Might overlap with yandere. Although there's no need for violence to be shown, only the expression.