This path is available in the help section of the game. On the main menu click “Help” then click “Paths” on the top row, and next to where it says “Things to do when you are naked” click “Enable”, then load up a save of pizza dinner or steak dinner. Correct choices will be highlighted in Magenta. Note: Where there is more than one choice, you might have to do one, then the other when you get to the choice page again. If you did not save an opening, enable “Pizza Dinner” or “Steak Dinner” as well and start a new game from the beginning.

Start with Pizza Dinner or Steak Dinner:

Go to the bedroom to put on a swimsuit
Change into a swim suit yourself
Go inside
Dance in the living room
Pick a Romantic playlist
Dip and kiss her neck
Change music
Pick a Rock playlist
Change music
Pick a Country playlist
Go somewhere else

Not only is this an interesting way to get her naked, it is the only way that does not block going for a drive downtown as an option. She will get dressed if you select it. Taking her shirt or top off while using the telescope will also not block downtown access. Both of these are cases of “spontaneous” nudity. Nudity involving the pool, hot tub or couch changes the mood of the date and Ariane won’t want to go anywhere far afterwards.

Go to the backyard
Go skinny dipping
Grab her boob
Just playing (Here is one we haven’t seen yet)
Lets swim some more 
Go Inside and Dry Off
Go to the convenience store
Go however you want
Let’s go in the store
Pay for the beer and head out
Go downtown
Go somewhere else
Take a shower
Follow her in the bathroom

The two of you are alone and naked, I’ll let you decide what to do next.