This abbreveation for "Dick in your mouth", is also used as a word to replace damn in sentences to people you have no respect for, but maintaining it's "dick in ya mouth" meaning.
Contrary to the chat room deffinition, this term was developed by a friend and myself over fifteen years ago, as a way to fuck with a guy at work who we had named "Dicknyamouf". Example. "Hey dicknyamouf, bring me a soda!"
"Diym nigga you gonna smoke the whole shit or what?"