“膝头哥挢眼泪”是粤语俗语，意思是屈膝抱腿，头伏膝上，泪流满面，形容悲哀伤心到了极点。常用来告诫别人，别做一些将来会后悔的事，到时候追悔莫及就要坐在地上痛哭用膝盖擦眼泪了。 事例： 1. 你唔好成日唔听人劝，唔认真读书，将来冇好嘅出路，到时候就只有膝头哥挢眼泪嘅份喇。（你不要总是不听别人劝告，不认真读书，将来没有好的出路，到那个时候就只有抱着膝盖哭的份儿了。） 2. 佢当初唔珍惜个段感情，依家爱人走咗，佢唯有自己膝头哥挢眼泪。（他当初不珍惜那段感情，现在爱人离开了，他只能自己抱着膝盖伤心哭泣。） 3. 唔好乱投资啲冇把握嘅生意，搞到最后蚀晒本，到时膝头哥挢眼泪都冇用。（不要胡乱投资那些没有把握的生意，搞得最后把本钱都赔光了，到那个时候再抱着膝盖痛哭也没有用了。）

"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.