derp Share definition Flag n. An obese man with a really fat egg head. They're usually bald and they have Harry Potter glasses. Person 1: EW LOOK AT THAT UGLY GUY!! Person 2: OMG, WHAT A DERP!! derp by Derp7 June 28, 2010 0 0 Get merch Get the derp mug. Buy Now — $32.95 See more merch