Play the game, and you'll see it.
If you're still in New Austin, then no need to ruin the surprise ;) Like the above comment says, play the game. Even if the nudity isn't really worth it xD.
I'm already in Mexico - so I must've missed it. Dang it. Someone help me out here.
It's a bit of a ways in.
It's before the end of the game but after Mexico. :)
You see a mexican girl's boobs. Calm down.