The Doctor makes a Dirty Joke when she first enters the Tardis

"So you decided to join me first rule no cloths for little humans." he says with a grin the bursts into laughter to make sure Rose knows its a joke.

"Haha okay so I'm tired where do I sleep?"

"Walk down that hallway the Tardis will show you the way.

As shes sleeping nude so her cloths can be washed she contemplates what the Doctor had said.