Main Plot: Penny invites everyone to a Halloween party at her and Leonard's apartment, which gets out of hand when some of the costumes get a bit too personal.
Subplot: Leonard is hurt that Penny can't seem to remember their first kiss on Halloween.
This episode includes examples of the following tropes:
- Call-Back: Leonard and Penny kissing on Halloween and her kissing him again on his birthday both play important parts in the plot.
- Coordinated Clothes: For Leonard and Penny's Halloween party, Howard and Bernadette go as Bert and Mary Poppins, while Raj and Anu go as Supreme Court judge Ruth Bader Ginsberg and the U.S. Constitution. Sheldon and Amy were going as Doc Brown and Clara Clayton, but instead they go as Howard and Bernadette as payback for Howard dressing as Sheldon earlier.
- Let the Bully Win: While trying to get Sheldon to apologize for the costume, Howard brings up the almost-trope-naming moment from Star Wars: A New Hope. When Sheldon asks if he's saying they should "let the Wookiee win", Howard agrees with the sentiment, even if he rejects the exact terminology being used towards his wife.
- Moment Killer: Stuart accidentally interrupts Leonard and Penny in the middle of a romantic moment.
- More Insulting than Intended: Amy dresses up as Bernadette for Halloween and mocks her high voice. This turns out to be a major sore spot for Bernadette, who's had to deal with this kind of teasing her whole life.
- Oblivious to Their Own Description: Sheldon has no idea who Howard is dressing up as until he's told, despite Howard doing a spot-on impersonation of Sheldon's quirks.
- Running Gag: The poor quality of the guacamole comes up repeatedly.
- Sacred First Kiss: After denying that she remembers her first kiss with Leonard the entire episode, Penny admits she did and gives the details to back it up. When Leonard questions why, she says it felt like an unworthy first kiss compared to the one on Leonard's birthday (given that she was still technically with Kurt and drunk at the time).
- Third-Party Deal Breaker: Invoked; Sheldon and the other guys sit down to watch Halloween; the others caution him that it's scary, but Sheldon insists he can handle it. As the opening credits are playing, in comes Amy and insists that Sheldon not see it, much to his disappointment...until they get into the hall, when it's revealed Sheldon sent Amy a text asking her to come in and get him out of seeing the movie
- Wholesome Crossdresser: Raj goes to work and the party as Ruth Bader Ginsburg. He's fine with Anu knowing this but asks the guys not to tell her he made the neckpiece himself.
- Worse with Context: When Amy goes to see Bernadette about Howard apologizing, Bernadette brings up the offensive things Sheldon has done and not apologized. Specifically, she mentions that Sheldon said her baby looked like Winston Churchill. When Amy tries to spin it as a compliment towards Neil, Bernadette flatly says that he said it about Halley.
