The main characters from "Knocked Up", Ben (Seth Rogen) and Alison (Katherine Heigl), do not appear in this "sort-of sequel", but references to both characters are made: A picture of Alison can be seen on the wall and Pete plays Scrabble on his iPad with Ben and later mentions getting marijuana cookies from Ben. Three other, more minor characters from Knocked Up, do appear in this movie as well: Charlyne Yi's character Jodi (an amiable stoner in Knocked up; now an employee in Debbie's store), Jason Segel's character Jason (one of Ben's best friends with a crush on Debbie in Knocked Up; now Debbie's personal trainer) and Tim Bagley reprises his role as OB/GYN Dr. Pellagrino.
Billie Joe Armstrong from Green Day makes a cameo in which he mentions that it's a pretty big deal when Glee buys a song. "Good Riddance (Time of Your Life)" by Green Day was purchased by Glee but never aired.
Pete (Paul Rudd) makes a joke comparing his sexual prowess to that of David Schwimmer (and Ross, Schwimmer's character from "Friends") in a way that makes it clear that he thinks that neither Pete nor Schwimmer are very good in bed. A spokeswoman for Schwimmer told the Chicago Sun-Times newspaper that Schwimmer was not asked beforehand if he would be okay with being the butt of that joke, but Judd Apatow clarified that he didn't mean anything insulting by it; just that Schwimmer is an example of a famous person who is more like Apatow. Paul Rudd was a regular guest star on "Friends" during the show's last two seasons.
Sadie is a big fan of Lost and Jack (Matthew Fox) is repeatedly shown on screen. In Knocked Up (2007), Ben is very disparaging about Matthew Fox, saying there is nothing interesting about him. Ironically, Paul Rudd was a self-described "mega-fan" of "Lost" when it was on the air.
Graham Parker's involvement with the film came about when one of Judd Apatow's friends mentioned to him that Parker had a blog and the most recent entry was about trying to get his music into films. The blog entry even had the sentence "Are you out there, Judd Apatow?"
During the scene when Paul Rudd's character Pete is having coffee with his friend Barry, they are talking about why Pete told Debbie about taking the Viagra. There is a song playing in the background, "Magnet and Steel" by Walter Egan. This song was also in "Overnight Delivery" with Paul Rudd. It was Paul Rudd's character (Wyatt Tripps) and Kimberly Jasney's love song.
When the family is in the car, Sadie is watching Lost. The episode she is watching shows an explosion where Jack is thrown from the impact. This episode of Lost takes place in the final season: season 6, episode 13. There are a total of 17 episodes in season 6. Sadie says that she has eight more to watch, but it should only be four. She also says there are 114 episodes altogether when there are 118 episodes total.
In the film, Sadie becomes obsessed with the TV Series "Lost." Dominic Monaghan, who played "Charlie Pace," in the series and Megan Fox who plays "Desi," in this film, played a couple in Eminem and Rihanna's music video "Love The Way You Lie."
The trivia item below may give away important plot points.
When Debbie's father excuses himself to leave Pete's 40th birthday party, Pete's father mentions to him that they'll see him again after the Cub's win the pennant. Going by the 7 year gap they had just discussed prior to this line, this means they would see him in 2019. Pete's dad was off by 3 years, as the Cubs finally won the pennant in 2016.