These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Knocked Up
Completely Missing the Point: A real-life example in that Katherine Heigl appeared to regret her role in the film (and went on to make more standard rom-coms like The Ugly Truth) because according to her, the film made her look stuck up because Allison didn't have fun and didn't mess around and get stoned like Ben and his crew, which misses the entire point of the film in that Ben is the one who needs to mature and get a real life to be actually worthy of being a father and being with her. The film does, admittedly, have less of an arc for Allison, but she has comparatively few faults compared to Ben, who really needs to shape up. Lampshaded heavily in a review of The Ugly Truth by Film Brain, who points out that that film treated its characters of both genders a hell of a lot worse than Knocked Up did.
Dude, Not Funny!: James Franco is less than amused by Allison's vomiting mid-interview.
"Funny Aneurysm" Moment: When Ben is exercising he says "I'm breathing like James Gandolfini here!" that became a lot less funny when James died of a heart attack in 2013.
Hilarious in Hindsight: In the film, Jason makes a joke about Jay wanting to "rear Ben's child". When the DVD came out with some deleted scenes, Jason reveals to Ben that he more or less wants to do the exact same thing! Of course he assumes the baby will be a girl, will look like her mother and he plans on waiting until she's 18.
Debbie mistakes one of Alison's pregnancy tests as her own and freaks out when it reads positive. In This is 40, Debbie really is pregnant!
Nightmare Fuel: Alison's niece describes what she thinks happens when a woman has a baby. It sounds even more horrifying than the real thing.
One-Scene Wonder: Craig Robinson as the nightclub bouncer that Debbie curses out for not letting her and Allison in.