NOT LONG INTO Joker: Folie à Deux – things are already going downhill and I’m honking mournfully in the pews – our sap of a hero meets his amour. He’s a manic headcase called Arthur Fleck, manacled in an asylum for sextuple murder; she’s called Lee and has a bad case of regrowth. “You know,” she says, “I must’ve watched that TV movie they made about you…