Simon feels as though the energy at school on Halloween, which is conveniently on a Friday, is infectious. He wears cat ears and a tail, and Abby comes home with him after school so they can carpool with Nick and Leah to Garrett's party. As Abby cuddles with Bieber in her Cleopatra costume, Simon notices that she seems unconcerned that her dress has ridden up to the tops of her thighs, and wonders if she knows he's gay. They make grilled cheese sandwiches and then sit with Nora in the living room. Nora makes herself a grilled cheese, and Simon beats himself up for not asking her if she wanted one.
When Simon is so caught up in the fact that he didn't offer Nora a sandwich, it shows that he does indeed have the capacity to think of other people and anticipate their needs—it's just not something that's automatic for him yet. This reinforces that he's learning how to become more empathetic and caring as he grows up and comes of age.
When they arrive at the party, Simon feels immediately alienated—kids are drinking alcohol, while he's used to parties with junk food and the game Apples to Apples. Leah declines Garrett's offer of alcohol, while Simon accepts a beer and Abby asks for vodka and orange juice. Nick runs to find a guitar, leaving Simon standing awkwardly with Abby and Leah. Leah is extra sarcastic in Nick's absence, and Simon feels as though the girls are showing off for each other. Garrett returns with drinks, teases Simon about his costume, and looks extra confused when Leah tries to explain she's dressed as a manga character.
The presence of alcohol immediately marks this party as being mature and adult, especially in comparison with Simon's innocent parties complete with junk food and kid-friendly board games. Again, this reinforces that Simon is growing up, and as he does so, the way that he celebrates holidays necessarily changes. His discomfort at this party, however, shows that this isn't necessarily a change that's easy to make or even something that's necessarily desired.
Two drunk girls slam piano keys and laugh, and Simon almost wishes he were home watching TV and eating candy with Nora. He finds his beer disgusting and marvels that people get fake IDs in order to drink it. Simon thinks better of Garrett when he goes and pulls the lid over the piano keys. Nick returns with a guitar and sits down. Simon, Abby, and Leah sit on the floor nearby. As Simon drinks, he thinks his beer isn't so bad. He watches people come over to listen to Nick and thinks about Cal Price, who he's pretty sure is Blue—when they look at each other, he feels as though they get each other.
Simon's dislike of the beer reinforces his discomfort with the changes he's undergoing as he grows up and comes of age. However, the fact that he continues to drink it even though he thinks it’s disgusting reveals that he feels pressured to grow up and conform to what his peers are doing. When he decides that Garrett might not be so bad because he rescues the piano from the drunken girls, it shows Simon actively expanding his conceptions of other people.
Simon starts twisting Leah's hair. He thinks it's pretty and smells wonderful, thanks to the beer—which he now thinks is wonderful as well. He tells Leah her face looks Irish, and proceeds to drunkenly remark on how crazy it is that everyone's ancestors are from all over the world. He tries to talk about where Abby is from and wonders if knowing nothing about Africa makes him racist. She answers that her ancestors were probably West African and they ended up in the U.S. thanks to slavery. Simon stops talking, and Martin awkwardly jumps up to get people more drinks. Simon muses that he and Leah don't drink and have never had sex, and he thinks that Blue is just like them.
Notice here that even though Simon is obviously intoxicated, he still groups himself in with classmates like Leah who don't partake in adult things like alcohol and sex. This again highlights that drinking isn’t something he particularly wants to do, but he bends to the pressure to be cool and fit in with his classmates. Also, the fact that Simon thinks of himself as someone who doesn’t drink—even though he’s currently drunk—suggests that he’s not fully aware of the changes he’s going through.
Abby pulls Nick up to dance. Martin jumps up too and insists that everyone needs to admire his dancing, which is extremely awkward. Abby tugs both boys onto the dance floor and then proceeds to dance by herself, leaving the boys to bob and sway near her. Leah watches this and tells Simon that this is more painful than what happened at Nick's bar mitzvah.
The mention of Nick's bar mitzvah, which would've happened when Nick, Leah, and Simon were thirteen, reinforces that the friends have history that in some cases makes it hard to understand or accept the changes happening right before their eyes.
At midnight, Leah drops everyone off at Nick's house and Abby and Simon walk to Simon's house. He observes the smashed pumpkins and toilet paper littering the sidewalk. Abby tells Simon that earlier that night, Martin brought up homecoming several times as though he was trying to ask her to the dance. Abby says she's already going with someone else and asks Simon to tell Martin. Simon agrees, and when Abby suggests he ask Leah to homecoming, Simon laughs and considers telling her that he's gay.
Abby is clearly aware that Martin has a crush on her (and doesn’t seem to reciprocate those feelings). It’s strange, then, that Simon is still trying to help Martin woo her. Though it's certainly understandable why he's going along with Martin's blackmail, the fact that Abby’s own feelings don't cross his mind illustrates just how caught up in himself Simon is at this point.
Mom greets Simon and Abby when they arrive with a plate of snacks. Abby tells her about everyone's costumes, and Simon quickly excuses himself to his bedroom to lie on his bed and listen to Elliott Smith. Simon decides he won't tell his parents about the party, since his parents are always shocked whenever he expresses a new interest or changes a little bit. He thinks that his parents make everything into a "big coming out moment," which he thinks isn't normal. Simon thinks that he's tired of “coming out” over and over again as he experiences small changes.
Simon's explanation illustrates why he was so caught up in Nora's ear piercings earlier: he likely learned this overbearing behavior from his parents. However, it's also worth noting that when his parents get overly observant and excited about the changes their kids are going through, Simon doesn't at all appreciate the attention. Just as in the case with Abby, this shows how caught up Simon is in thinking about himself and not thinking about how his actions impact other people.