Laws of Lunch

The Tenth Doctor once offhandedly claimed to Donna Noble that the Laws of Lunch overruled the Laws of Time, defending his actions in saving Lobus Caecilius and family from the eruption of Mount Vesuvius, at the fall of Pompeii.

Specifically, he felt it would be rude to let someone die after they offered him a "nice lunch", as did Caecilius. (PROSE: The Fires of Pompeii)