「膝頭哥撟眼淚」是粵語俗語，意思是屈膝抱腿，頭伏膝上，淚流滿面，形容悲哀傷心到了極點。常用來告誡別人，別做一些將來會後悔的事，到時候追悔莫及就要坐在地上痛哭用膝蓋擦眼淚了。 事例： 1. 你唔好成日唔聽人勸，唔認真讀書，將來冇好嘅出路，到時候就只有膝頭哥撟眼淚嘅份喇。（你不要總是不聽別人勸告，不認真讀書，將來沒有好的出路，到那個時候就只有抱着膝蓋哭的份兒了。） 2. 佢當初唔珍惜個段感情，依家愛人走咗，佢唯有自己膝頭哥撟眼淚。（他當初不珍惜那段感情，現在愛人離開了，他只能自己抱着膝蓋傷心哭泣。） 3. 唔好亂投資啲冇把握嘅生意，搞到最後蝕曬本，到時膝頭哥撟眼淚都冇用。（不要胡亂投資那些沒有把握的生意，搞得最後把本錢都賠光了，到那個時候再抱着膝蓋痛哭也沒有用了。）

"Using the knees to wipe away tears" is a Cantonese saying. It means bending the knees, hugging the legs, resting the head on the knees, and having tears streaming down the face, which describes being extremely sad. It is often used to admonish others not to do things that they will regret in the future. Otherwise, when they are overwhelmed with regret, they will have to sit on the ground and cry while wiping their tears with their knees.