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: 不要評論一個人在聚會/餐館/餐桌上喫得有多少：這對當事人來說是一種令人難以置信的負面體驗，許多人由於殘缺的、悲慘的疾病而無法一次喫下正常的分量，即使是他們最親近的親人也沒有注意到。