It’s in the asylum where Joker would have done the ‘damaged’ tattoo as a message to Batman saying, ‘You’ve damaged me.
David Ayer spoke to Empire and explained that The Joker’s metallic teeth and his “damaged” tattoo both have roots in Batman’s A Death in the Family storyline.
But Joker killed Robin and Batman basically smashes his teeth out and locks him up in Arkham Asylum.
We’ve seen the sort of punches that this new Batman can throw, so Joker must have received quite a few.