Caution: Spoilers ahead for Joker.
Joker's version of Thomas Wayne wouldn't approve of the Batman fighting crime in Gotham City. Set in the 1980s, Joker finds Thomas Wayne in his pomp as the city's premiere billionaire celebrity, a figure of philanthropy and an aspiring mayor. Though only a peripheral character, Arthur Fleck spends much time musing over Thomas Wayne and the two have a fiery confrontation, all of which serves to demonstrate that the version of Bruce's Dad seen in Todd Phillips' movie is quite different to the standard depiction of the character. Traditionally, Thomas Wayne is a figure of virtue - someone Bruce reveres for his kindness, social awareness and desire to help those less fortunate.
In Joker, Thomas Wayne's motivations come across as more morally ambiguous. Wayne's campaign to become mayor has distinctly self-serving undertones and his "do you want an autograph?" line when first meeting Arthur Fleck demonstrates an unlikable arrogant streak. The founder of Wayne Enterprises also appears to have a less sympathetic attitude towards Gotham's working class, assuring them that he's the only man who can drag them from poverty to salvation in a speech that is either political drivel or evidence of a growing god complex. Unlike the reluctant billionaire of previous stories, Joker's iteration of Thomas Wayne represents the establishment, verbally putting protesters down instead of attempting to sympathize.
This kind of attitude already puts Thomas Wayne at odds with his son's principles and values, since Batman is known as a far more forgiving, selfless and universal public figure than his father. However, the real proof that Thomas Wayne would strongly disapprove of the Batman - if he were alive to see his son take to the streets - comes when the Joker character condemns the subway murders that trigger the clown protests. Wayne strikes out at the murderer (secretly Arthur Fleck) for wearing a mask while committing the crime. The billionaire goes on to rally against the idea of someone taking to the street in a mask, branding them a coward.
Obviously, masks are Batman's whole thing, and although the DC superhero is fighting crime instead of committing it, acting as an anti-establishment vigilante who conceals his identity is unlikely to go down well with Joker's interpretation of Thomas Wayne - even more so if he knew his own son was the man behind it all. This implied dynamic between father and son highlights just how much Joker shifts Thomas Wayne away from the character's usual template. In one DC comic reality, Thomas himself even becomes frustrated with Gotham's justice system and goes out onto the streets to try and right some wrongs.
Of course, it must be noted that the version of Thomas Wayne the audience sees in Joker comes via a highly unreliable narrator. The film is entirely told through the eyes of Joaquin Phoenix's character and there is plenty of evidence to suggest that the majority takes place in Arthur's head while he occupies a padded cell. Under these circumstances, Arthur obviously bears some kind of grudge towards Thomas Wayne and would be sure to paint him in a harsher light than Batman's Dad might deserve in reality.
