Fridge Brilliance: Mary says that she and Hancock are siblings. He says "That's a lie - brothers and sisters don't kiss the way you kissed me last night". But moments before she said that they were known as gods in some cultures. Now take a look at the family tree of almost any major pantheon. It is entirely possible they were married and siblings.
Fridge Logic: When Hancock has sex in the Unrated Cut, it ends up being Destructo-Nookie, and he almost kills his partner. How was Mary able to conceal her powers since she was married?