Broken Sword 3: The Sleeping Dragon Easter Egg - Secret Paris Area

After leaving Vernon's apartment for the first time, you should see a skater boy. You must do this egg now, because later in the game the skater boy will disappear. Walk up to the skater boy and use the lipstick on him. Nico will say "There was no way I was going to do that!" or something similar. You have just triggered the easter egg. Now walk down the street until you pass the park. Normally, when you walk pass the park, Nico will say "I considered leaving the area," and the game will ask you where you want to go. If you used the lipstick on the skater boy, it will go right into a loading screen as soon as you past the park. After the game is done loading, you'll be in the secret area. There isn't much to do here, but there is a dog that walks around. There is also a bridge that goes over the river. If you walk down the bridge far enough, Nico will say, "I considered leaving the area," and the game will ask where you want to go.

By the way, this easter egg is the only use for the lipstick in the whole game.