DAYUM Share definition Flag What a guy says when a hot girl walks by, especially if she has a round booty. "Dayyyyyyyyum, did you see that?? I'd like to put my cock into that fine piece of meat there!" DAYUM by thatgirldrinkinglemonade July 8, 2003 0 0 Get merch Get the DAYUM mug. Buy Now — $32.95 See more merch