Simon emails Blue and tells him that he's never worn a scary costume for Halloween before; his family only does funny ones. He wore girls' dresses until fourth grade when suddenly, he was mortified to see himself in a flapper dress. Simon comments that by not dressing up, Blue is throwing away an opportunity to be someone else for a night. Blue replies that he loves dressing up and was a superhero every year as a kid, but he's not going out this year. He has to sit at home and give out candy—Blue’s mom will be away at a work party. Blue comments that Simon was surely a great flapper and asks how his parents were about buying dresses. Blue tries to guess what Simon's costume is, but the conversation fizzles when Simon's phone embarrassingly autocorrects to sexual and suggestive language.
Blue's love of dressing up as a superhero every year for Halloween introduces the idea that both Simon and Blue hide their true selves and project an entirely different identity in their day-to-day lives—much like being a superhero or wearing a costume, both Simon and Blue mask the fact that they’re gay. When Simon talks about wearing a scary costume for the first time and Blue talks about not dressing up, it shows that the way that both boys experience this holiday is changing as they grow up, mature, and their own families change.