The baby turning around to look at Mac (Seth Rogen) and Kelly (Rose Byrne) having sex in the first scene of the film was accidental. The scene was originally supposed to end after Seth Rogen turned her around. However, Director Nicholas Stoller noticed that the baby kept looking around to watch Rogen and Rose Byrne, so he instructed one of the camera men to film the baby. According to Stoller, if you listen closely, you can hear Rogen and Byrne laugh after the baby turns around to watch them.
The entire cast and crew became very attached to the twin baby girls Elise Vargas and Zoey Vargas, who played Stella. The entire cast and crew went to the set on the babies' last day of filming, so they could say goodbye to them.
The film was originally written as Mac and his friends going against the fraternity, but after Seth Rogen's wife read the script, she said that his friends would not care about the fraternity war, and suggested writing Mac's wife into the script instead.
According to the actors, actresses, and Nicholas Stoller, the twin girls Elise Vargas and Zoey Vargas, who played Stella were incredibly well behaved, and were always smiling and happy. The only time one of the babies became upset and started to cry was when Seth Rogen and Rose Byrne yelled at each other, while filming their fight scene.
The film earned its production budget back on the first day of the film's theatrical release in the United States. The budget was eighteen million dollars, and the film made 19,574,490 dollars on its opening day.
The film is titled Bad Neighbours in Australia, New Zealand, the United Kingdom, and The Netherlands to avoid confusion with the television soap Neighbours (1985). A video was posted on Universal's Facebook page, showing Seth Rogen singing the theme from the show.
The writers wanted the fraternity boys to be as lovable as possible, and avoid portraying them as the typically obnoxious, Revenge of the Nerds (1984) kind of bullies. They interviewed many of their own friends, who had been in fraternities, to get an accurate picture of frat life. These interviews were also the source of many of the hazing rituals seen in the film, but some of the rituals, of which they learned, were so shocking, that they could never be depicted on-screen.
The song being played at the frat party, when Mac first calls Teddy to try and get them to turn the music down, is the same song from Get Him to the Greek (2010) that Sean Combs refers to as a "game changer."
In the hazing scene, where the pledges are forced to wear animal masks and walk in a circle naked, "assjuice" tells Teddy (Zac Efron) "I am not an elephant, I am a human being" this is a reference to The Elephant Man (1980).
When Mac and Teddy are intoxicated, they begin speaking in their favorite Batman's voice. The quotes that Teddy uses are from The Dark Knight (2008) when Batman interrogates the Joker for Harvey Dent's whereabouts.
Seth Rogen (Mac) and Randall Park (the AT&T recruiter during the college convention) although not in the same scene in this movie, starred together in The Interview (2014). Park plays Kim Jong-un, while Rogen is James Franco's show producer.
This film opened in the UK on a Saturday, May 3, 2014, instead of the normal weekday opening day of a Friday. Several UK cinema outlets started their first showings at midnight or a few minutes after midnight.
Part of the reason that Dave Franco was cast in a major role in this film was that Seth Rogen felt bad that he wasn't able to cast Dave alongside his brother James in "This Is The End", due to the Apocalyptic setting of that film mandating that Dave's character would have had to be brutally killed off in front of James and Rogen saying that was too depressing. Rogen wanted Dave to get a major spotlight role and pushed successfully for him to be cast in this film.
This movie indirectly caused a very public spat between Seth Rogen and the Washington Post's film critic Anne Hornaday. After an angry, unpopular and misogynistic British college student in California murdered several people, Hornaday seized on the news that he'd watched this and many other Rogen films and speculated that Rogen was responsible for his actions because they didn't reflect the reality of social loneliness for someone who was awkward and not conventionally good-looking. Rogen angrily responded that Hornaday was saying he caused a tragedy by "getting girls in movies", and Judd Apatow publicly called Hornaday's theories "idiotic" and said she was trying to assign blame to a larger cause than the situation warranted.
Paula suggests Mac and Kelly drop their baby at the fire station, which happened in Breaking Bad (2008), which is referenced in this film. Also, Seth Rogen starred with one of Breaking Bad's stars Jesse Plemons in Observe and Report (2009).
Zac Efron broke his hand during his fight scene with Dave Franco. The writers and producers were panicking, and started to plan how the broken hand would fit into the movie, and how much the budget would change. However, they were surprised to learn that Efron arranged an emergency surgery, so he could be back on-set one day later.