How do you get your sim naked in Sim 2

While you are in the neighborhood type in: boolprop testingcheatsenabled true
Then pick your lot, hold down SHIFT and click on your sim.
It will come up with many options. In the top right hand side there will be the option, 'Change Suit'.
Then choose the option 'Underwear or naked'
However, the sim will only have a blur instead of having "parts". There's a link for removing the blur in Related Links, but that will only remove the blur and you will be left with a slightly creepy, undetailed, smooth skin. If you want your sim to have "parts", then Google "naked sims 2 mesh". I won't post a link because there are kids on this site. Naked meshes will give your sim "parts" instead of smooth skin.