: While hosting the party, Leonard and Penny argue over the date of their first kiss. Leonard remembers it happening at a Halloween party years prior, while Penny insists it was at his birthday party.
The identifier "711-S12-E06-TBBT" refers to Season 12, Episode 6 of , titled "The Imitation Perturbation" . Watch 711-S12-E06-TBBT
The Imitation Perturbation | The Big Bang Theory Wiki | Fandom : While hosting the party, Leonard and Penny
: Penny eventually admits she does remember the Halloween kiss but wanted to "erase" it because she was drunk and only did it to make her ex-boyfriend, Kurt, jealous. She prefers to count the birthday kiss as their "official" first because it was the first time she kissed him because she truly cared for him. Costume Summary Initial Costume Party Costume Sheldon Doc Brown ( Back to the Future ) Howard Wolowitz Amy Clara Clayton ( Back to the Future ) Bernadette Rostenkowski-Wolowitz Howard Sheldon Cooper Bert the Chimney Sweep Bernadette Mary Poppins Leonard Inspector Gadget Inspector Gadget Raj Ruth Bader Ginsburg Ruth Bader Ginsburg Penny German Barmaid The Imitation Perturbation | The Big Bang Theory
: Howard Wolowitz decides to dress up as Sheldon Cooper for Halloween at Caltech. Sheldon is initially oblivious, but once he realizes everyone is laughing at his personality quirks—rather than with him—he feels deeply insulted and hurt.
The story of this episode centers on a Halloween conflict and a sentimental revelation between the main characters:
: After Bernadette refuses to make Howard apologize, Amy Farrah Fowler encourages Sheldon to seek revenge. They arrive at Leonard and Penny's costume party dressed as Howard and Bernadette . Amy delivers a particularly sharp, high-pitched impression of Bernadette's voice and abrasive personality.