The 31-year-old actress discovered a love of late-night clubbing while recently filming a movie in Montreal, Canada and has reverted to her younger self by staying up all evening and "losing her mind".
She said: "I`d go completely sober and just dance. It`s like literally losing my mind.
"It`s payback time. When I did a Bond film, everyone thought I was 30. So now if I want to behave like a 21 year old, I f***ing well will."
The `Made in Dagenham` star used to find she wanted to fit in, but growing up has taught her she is not "normal".
She said: "Back then, I wanted to be as normal as possible. Now, I don`t mind not being normal, I realise I don`t fit in."
Despite being famed for her beauty, London-born Rosamund doesn`t believe it was the case when she was a child.
She told Culture magazine: "I am the last person to think of looks before personality. I spent my teenage years relying solely on wit because I never looked sweet and girly enough for boys. Words were my weapons."