Theroy on The Joker The Joker being a formaer Robin gives us a whole new dynamic with the archrivals' realtionship. As Mentioned earlier, it would give us a reasonable explation as to why Leto's Joker looks like a god damned juggalo.
The thought of the kind of Joker we're normally familiar with, sitting down in a tattoo parlor for hours, days on end to get all that ink is frankly a little bit laughable. But what if each tattoo wasn't for the Joker, but for Batman? Sure, the J on his cheek could stand for "Joker," if this guy is super into personal branding, but what if it's a reminder that he's still Jason? An even more blatant message is scrawled on his right arm, where we can see a few feathers of what is presumably a tattoo of a bird -- probably a robin. You could extrapolate meaning from every tattoo; does the skull in a jester hat make sense if Joker ripped it off of a poison POG from the 90s, or might it represent Jason Todd's "death" and rebirth into the maniacal jester as shown in Suicide Squad?