When you get a boner and ejaculate at the same time.
(verb) I duke nukem whenever I drink whiskey and put my wiener in strange places.
(noun) I had a Freudian dream last night where I blew up a submarine. I was informed in said dream, that when one becomes erect and immediately ejaculates, it is referred to as a duke nukem. When I awoke, my boxers were covered in semen. I clearly had experienced a duke nukem.