To loaf or evade duty; also, to bungle or botch. This term dates from the first half of the 1900s and became widely current during World War II. Early on it also was slang for male masturbation, but that sense has not survived. John Hersey used it in G.I. Laughs (1943), “Wanders from barracks to barracks . . . generally flubbing his dub.” And D. Stagg (in Glory Jumpers (1959), “The Air Corps flubbed the dub again and scattered the drop.”