The baby turning around to look at Mac and Kelly 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 the 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 the director, 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 & 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 film's actors and director Nicholas Stoller, the twin girls Elise Vargas & 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 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.
When the frat looks back at the toga party and beer pong creation, the actors playing the guys in togas are The Lonely Island and the actors that discovered the beer pong are from the TV show Workaholics (2011).
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 they learned of were so shocking that they could never be depicted on screen.
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.
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 Zac Efron "I am not an elephant, I am a human being" this is a reference to the 1980 film The Elephant Man (1980).
Seth Rogen (Mac) and Randall Park (the AT&T recruiter during the college convention) although not in the same scene in 'Neighbors', 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 - 3rd May 2014 - instead of the normal weekday opening day of a Friday. A number of UK cinema outlets started their first showings at midnight or a few minutes after midnight.
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.