Context: Chanmari ちゃんまり claims to be extremely tareme, proceeds to define tareme, and then disprove that she is tareme according to her own definition of tareme.
{megashira to mejiri wo tsunaida} sen ga suihei ika nara tare-me 目頭と目尻をつないだ線が水平以下ならタレ目
If the line [that] {connects the inner corner of the eye with the outer corner} is less than level, then it's tareme.
suihei 水平
Level. In the sense of perfectly horizontal. Literally "water-flat," probably because the surface of a body of water is level.
