someone who is so stupid you cant even explain it so you have to use the word dumb fuck to describe them which is even more stupid. this word is only used for those that dont even deserve a real insult.
eric: *bikes into a car*
arjun: WOW UR THE DEFINITION OF DUMB FUCK!!!
eric: wut?
arjun: no seriously go to urbandictionary.com...becuz ur now the definition for dumb fuck