DNFU Share definition Flag DNFU is an acronym meaning "Do Not Fuck Up", usually being said by one's superior when the subject in question is discovering new terrain. "Here are the keys to my Ferrari, i really need you to get those cigarettes so DNFU." DNFU by Rashudo October 20, 2007 0 0 Get merch Get the DNFU mug. Buy Now — $32.95 See more merch