* Let it be known that Duke is a man of his word. When he tells the Overlord that he'll rip his head off and shit down his neck, he does exactly that in the closing cutscene, [[ToiletHumor even pulling out a newspaper to read as he does his business...]] all while whistling his own theme tune, "Grab Bag"!
* In the Mirage Barrage level from the 20th Anniversary World Tour:
--> '''Duke''': [[Film/TheDarkKnight Why so serious]], [[VideoGame/SeriousSam Sam]]?
* A classic: "Your face, your ass; what's the difference?"
* In some levels, you can interact electric sockets, taking shock and little damage. If your HP reaches 0 while doing this? You explode into bloody mess.
* Earlier versions of the game allowed you to use Duke's left-leg [[EmergencyWeapon Mighty Foot]] and his unarmed right-leg kick at the same time. The result is that it looks like Duke is running around killing aliens with ThatRussianSquatDance (or, if you prefer, [[Franchise/MortalKombat Liu Kang's bicycle kick]])
** And a common joke about it is that he uses his "third leg" to support himself for those kicks.