A person who invents an unfunny and unnecessary word or phrase in order to submit it to Urban Dictionary as the lone contribution that individual will ever make to society, all in the vain hopes that said Dumbfuck will have started a word or phrase which will spread like wildfire among the English language.
The Dumbfuck typing into Urban Dictionary: "'Facebalking' means you are hesitant to put something on Facebook!"
Friend: "That is the stupidest word I've ever heard. Did you make that up just to put something on Urban Dictionary? You are a total Dumbfuck."