As a threat: dfwm buddy!
In response to a statement made by someone who is trying to kid you: "Hey man, I won the lottery today!" "dfwm"
In response to any statement made by anyone at any time. "Hey, how are you?" "dfwm"
a welsh slang word merging the words "dwi ddim yn gwybod" (i don't know) into one lazy outburst instead of using the actual language. Normally used by people from Caernarfon that have nothin better to do than sit around Safeway car park