If Duke could, he would rip those controls from your hands and smack you for even thinking about cheating. At least try to play without cheating—you owe it to Duke (and to the developer, who put so much time and effort into the play-balancing of this game to make it worth your while). However, if you just can't play Duke Nukem 64 like it was intended to be played, then here are the Cheat codes for you, Princess. Try not to break a nail using them.
L = Left shoulder button
R = Right shoulder button
C = C pad buttons
J = + pad buttons
Enter these codes from the main game menu. You will hear a sound effect to let you know that each one is active. To use them once they are active, go to the Cheats menu and turn on the ones you want, then press the START button.
LJ, LJ, L, L, RJ, RJ, LJ, LJ
R, RC, RJ, L, LC, LJ, RC, RJ—Gives all items
R, R, R, R, R, R, R, LJ—Nothing can hurt you, but you can get stuck in crushing spots and have to restart
L, LC, LJ, R, RC, RJ, LJ, LJ—No monsters
L, L, L, RC, RJ, LJ, LJ, LC—Change levels at will