Cantonese slang for the direct English translation of 'Mother Board'. Proper Cantonese term is Dai Barn (meaning bottom board or lower board). Lo Mo means mother but is a rude way to say it and can be interpreted as swearing.
"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!"