Batman has been around for 80 years. That leaves a lot of material to mine for Easter Eggs, and most Bat-media is chock full of them. But director Todd Phillips was bound and determined to keep his standalone Joker movie as Easter Egg-free as a vegan frittata at a Satanist brunch.
Prior to Joker's release, Phillips was adamant that there were zero Easter Eggs hidden in the film, at least none that he was responsible for. He went so far as to say that anything fans found in the movie was either a mistake, or the art department trying to troll him. That seems strangely hardline for a comic book movie. But if you listen to the director's commentary, Phillips admits, "I just don't like that term, 'Easter Egg,' but little Bruce there when he slides down the pole, was that an Easter Egg to the Batman television series? And yes, in fact, it was. It was something we spoke about and thought, 'Oh yeah, why not do it?' Without being too cute, we don't like to do a ton of that stuff, but it felt appropriate."