If you go inside of your TARDIS and then use the Stattenheim Remote your TARDIS materializes inside of itself. When the TARDIS materializes the client says "Now now, Don't be silly." When you try to open the client says "Are you uh...mad...?" 

By the way, DO NOT use the flight panel. You'll get softlocked and you won't be able to exit.

Actualy the tardis inside the tardis is not a easter egg, its a bug that probaly will be fixed in the patch.

 I meant the things that are said when the TARDIS is inside the TARDIS.