What Happened To Everyone Who Dated Joker?
2. Thomas Wayne - Flashpoint: Batman
As much as having our universe's Joker in a clandestine affair with Batman's father would be suitably hilarious, this isn't quite the case.
Instead, this relationship takes places in the Flashpoint universe, which has Bruce Wayne be the one shot down by Joe Chill in that infamous dark alley, and his parents the grieving survivors of the tragic attack. After Martha convinces her husband to find and kill Chill, she goes for a swan-dive off of the deep end, turning into that universe's Joker - resulting in Thomas being the one to take on the mantle of the Dark Knight.
It's an unusual storyline to be sure, but it also works uncannily well, as it blends the regular Batman and Joker rivalry with the love that the married couple still clearly have for one another.
While the Flashpoint Joker is dead, her partner is still canonically alive in the main DC universe, currently the antagonist of the City of Bane Batman storyline.