To get the naked girl ending you have to beat the game 10 times in a row on the hardest setting while only using kick and you also have to not kill any lizards. If you do this you will get a movie with the lady from the strip club on level 2 show off her whole body and have sex with duke nukem! Thanks to my friend Josh school for this one
This secret also lets you use the BFG from doom and it works just like it does in Doom. To do it go to the doom guy on level 3 which is behind the church and jump on top of him 69 times. If you do that the doom guy gets up and then you are the doom guy and can shoot the BFG like in Doom. Also you are naked. Thanks to Tim at school.
While in the game type DNCORNHOLIO and you will become god and be able to shoot balls from your hands that kill enemys.