It's a line from the end of The Doctor Dances from Christopher Eccleston's time on Doctor Who, as written by Steven Moffat.
https://www.youtube.com/watch?v=GMXrzKkpnRoVideo can't be loaded because JavaScript is disabled: Red Bicycle When You Were Twelve (https://www.youtube.com/watch?v=GMXrzKkpnRo)
Rose Tyler: You, beaming away like you're Father Christmas!
The Doctor: Who says I'm not, red-bicycle-when-you-were-twelve?
Rose Tyler: What?
When Russell T Davies got[...]
