The day after August's birthday party, Summer asks what he's going to be for Halloween. She explains that they can wear costumes to school. August is thrilled that he can be Boba Fett from Star Wars, but is upset when Summer explains that they can't bring guns or blasters. She explains that she's afraid her preferred costume might be too dorky. She says that Savanna's group isn't even wearing costumes because they think it's stupid and immature. Regardless, Summer really wants to be a unicorn. August agrees that a unicorn would be dorky but says she should do it anyway. Summer decides she'll just go as a Goth girl.
Summer's struggle to decide on a costume is indicative of the social landscape at school. Even though Summer is clearly eschewing any hopes of being popular by eating lunch with August in the first place, it's also telling that she feels the need to preserve some of her social standing by choosing a socially acceptable costume. Her mixed feelings about the unicorn costume also shows that she’s torn between wanting to be a child (who likes unicorns and wants to dress up as one) and wanting to be more of an adult (who thinks unicorns are “dorky”). Her choice to go as a Goth girl feels like a sharp contrast from her original desire to be unicorn, showing that she’s bending to what other people think and perhaps acting in a way that’s not true to her.