"Diu Nei Lo Mo!" ("fuck your mother") is a highly offensive profanity in Cantonese when directed against a specific person instead of used as a general exclamation. In contrast to the English phrase "fuck your mother", which indicates that the person being attacked commits incest with his own mother, the Cantonese expression has the implied meaning of "I fuck your mother".
Peter: "This song reminds me of my girlfriend back in Guangzhou."
Joel: "That song reminds me of your girlfriend too, if you know what I mean."
Peter: "DIU NEI LO MO!"