YSK: Don't comment on how little someone eats at a gathering/restaurant/dinner table: it is an incredibly negative experience for the person involved, many people cannot eat regular portions in one sitting due to crippling, tragic diseases that go unnoticed by even their closest loved ones.
from /r/YouShouldKnow
YSK: 不要评论一个人在聚会/餐馆/餐桌上吃得有多少：这对当事人来说是一种令人难以置信的负面体验，许多人由于残缺的、悲惨的疾病而无法一次吃下正常的分量，即使是他们最亲近的亲人也没有注意到。