On the bridge, David is reading the lyrics of "I Feel Pretty" from a script. The script is bound by a paper clip that changes to a staple and back to a paper clip between shots.
Adam Sandler's sideburns change lengths throughout the film, particularly when he is first boarding the airplane. When he is saying goodbye to Linda, they are longer, and then they become shorter when he is on the plane.
When David is in the car with the prostitute, he starts recording the encounter after she sings "I feel like dancing!" However, when David is talking to his lawyer, the recorder replays the singing, which was not recorded.
When Dave and Dr. Rydell sit in the plane, we see a middle row of seats (i.e. two aisles). The exterior view of the plane shows a Boeing 737 which doesn't have a middle row.
The game has not started yet but as Bob Sheppard says your attention please before the game, you can clearly see the scoreboard and Boston is up 2-0 in the 8th inning,
The screening of Tomcats (2001) on the plane jumps between scenes out of chronological order each time the screen is shown.
When Dave walks in on Andrew in the bathroom, Andrew tells Dave that he's watching a bass fishing program. The shot at the end of the scene show a brown trout, not a bass.
The airplane shown from the outside is a 737, but the interior shown is a 2 5 2 aisle configuration, which is not a 737 option.
In the Yankee scoreboard scene, 1-800-BUDDY would be 2 digits short.
When Dave stands on Andrew's head in Frank's office his shoes can be heard making a sound that would come from a hard soled shoe making contact with a solid surface, yet prior to this when Dave and Andrew enter Frank's office no sound can be heard from their shoes as the office is carpeted.
Opening scene is set in 1978 yet the main character wears a The Dukes of Hazzard (1979) t-shirt from no earlier than 1979.
When Dave gets his pants pulled down in 1978, he is wearing late-1990's Fruit of the Loom underwear.
The opening sequence is dated Summer 1978 but the background song "Heart of Glass" by Blondie/Debbie Reynolds was released 6 months later, in January 1979.
While Dave is on his cell phone in the airport, his boss hangs up on him. You can hear a dial tone coming from Dave's phone. Cell phones don't have dial tones.
Buddy throws away Dave's CD's, which make a breaking glass sound.
When Dave is talking to Linda at the new york yankees ball game she utters the line "That wasn't so bad was it" but her lips only says "That wasn't so bad"
In a sunny shot of the outside of Dave's apartment building, we see an obvious shadow of a camera operator on a lift.
In the Buddhist monastery Dave refers to The Buddha as God, Buddha is not a god, he was the founder of Buddhism.
Dr. Rydell makes a mockery of the Buddha, asking how can a man weighing 600 pounds teach people about self-discipline. While some statues depict the Buddha as a fat man, many other statues depict him with an average build. In fact, the Buddha spent much of his journey towards enlightenment as a beggar, practically starving. Some statues depict him looking very bony in remembrance of this time in his life.
In the scene where Dave is telling Dr. Buddy that his mom is in the hospital, Adam Sandler, calls Buddy "Jack".