In the scene in London, when Dom is racing Letty, there is a little Asian boy who is seen watching the race from a double decker street bus. The same kid was shown watching Dom and Brian while they pulled the safe in the previous movie, Fast 5, it is Justin Lin's son.
When Hobbs arrives at the barbecue Roman remarks that they "better hide the baby oil," to which Hobbs replies with "you better hide that big ass forehead." Hobbs line was improvised by Dwayne Johnson, so Ludacris spitting out his drink and Tyrese Gibson being at a loss for words are both genuine reactions.
Dennis McCarthy, the man behind building the vehicles used in the franchise, says that they used "a whole fleet of BMW M5s" in order to complete one sequence. McCarthy also said "We pretty much destroyed every single one later on, in other scenes"; cars that appear on-screen in close-ups or action shots are not BMW E60 M5s.
An early leaked version of the Superbowl television spot showed the title "Furious 6" as the title of the film. The later released teaser poster and television spot showed the final title of the film. Justin Lin clarified that Universal Studios made the decision to promote the film as "Fast & Furious 6", the official title IS "Fast & Furious 6".
During the film Hobbs (Dwayne "The Rock" Johnson) is mocked by being referred to as a superhero three times, one of which is Thor. Elsa Pataky (who plays Hobbs Right hand woman) is actually married to Chris Hemsworth who plays Thor in several movies.
During the scene where Hobbs and Roman exchange jabs at the barbecue and Tej spits out his drink in laughter you can see a bottle of Conjure cognac on the table (presumably the same as what is in his glass). Conjure congac is an alcoholic beverage that Chris "Ludacris" Bridges (the actor who plays Tej Parker) actually co-owns.
Following Paul Walker's death on November 30, 2013, Universal announced that a portion of the profits from the film's North American Blu-ray and DVD sales, would be donated to Walker's charity Reach Out WorldWide.
Dwayne Johnson makes at least two direct references to his wrestling past. During one conversation he says "guaran-damn-tee," which was on of his mainstays in cutting promos as The Rock. He also states he wants to come down on Shaw like the Walls of Jericho. Biblical references aside, Walls of Jericho is a signature finishing move of fellow wrestler and musician Chris Jericho.
The Fast and Furious and X-Men franchises have often released the same installments of a franchise in the same year. X2 and 2 Fast 2 Furious were both released in 2003, X-Men: The Last Stand and The Fast and the Furious: Tokyo Drift were both released in 2006, X-Men Origins: Wolverine and Fast and Furious were both released in 2009, X-Men: First Class and Fast Five were both released in 2011 and The Wolverine and Fast and Furious 6 were released in 2013. Furious 7 was set to be released in 2014, the same year as X-Men: Days of Future Past, however it then was pushed to 2015 after Paul Walker's death.
When Tej and Hobbs go to the classic cars auction in London, Tej sarcastically makes fun of Hobbs purported knowledge about cars, with the line "He reads the brochure. I'm proud", after Hobbs comment about horsepower and number of cylinders. That line is almost the same used by Sean Boswell in Tokyo Drift, when he sarcastically answered to a provocation by an arrogant high schooler. Sean's line was "Wow. You can read the brochure" after the high schooler commented about horsepower and exhaust system.
Ludacris says the line, "Time is money," while he and The Rock are taking the clothes and watch off of the snobby auction organizer. This is the second time Ludacris said this line in his film career. The first time was in Crash (2005).
The trivia items below may give away important plot points.
When Letty is with Dom, Brian, and the crew towards the end of the film, Brian approaches Letty to apologize to her for getting her involved with Braga and Letty says to Brian, "I may not remember anything, but I do know one thing. Nobody makes me do anything I don't want." This is the first time in the entire Fast and Furious franchise, that Brian and Letty talk to each other directly.
Jason Statham and David Tennant were, at different points, considered to play the film's antagonist before Luke Evans signed on. Statham would go on to play future antagonist Deckard Shaw during the end credits scene, as well as playing him in Furious 7 (2015) and The Fate of the Furious (2017).
The brother Shaw quotes as teaching him "every man has a code" is presumably Jason Statham's character, who appears in the post-credits scene and features prominently in Furious 7 (2015) and The Fate of the Furious (2017).
The tunnel used in the chase scene when Brian's car is flipped is actually the Wallasey tunnel. One of the three Mersey tunnels in Liverpool. When Dom and Hobbs exit the same tunnel while chasing Shaw, they exit onto Wembley Way in London which is a pedestrianised street that leads to the famous Wembley Stadium.