In the pizza shop after John is jogging he is talking to Nedderman his
shirt is covered in sweat, but in the next shot it is not, and then in the next shot the sweat is back, then the sweat is bigger and then it gets smaller.
Kyley Baldridge, who plays young Young Farley, is blue eyed when Seann William Scott has brown eyes.
When John Farley is about to be interviewed by Tyra, they cover up his face wounds with makeup. Then he talks to his mom, in the same room, and they are uncovered. He goes back to sit down and one is covered with makeup again. Then he leaves, and they're both uncovered.
When Farley and Mr. Woodcock are in the barber shop, the
barber uses the clippers to make a huge, very noticeable bald spot in the back of Farley's hair. When he's getting out of the van at Mr. Woodcock's ex-wife's house, there's no bald spot. Then as he's walking to the door, the bald spot is back.
In the pizza restaurant, in one scene John hits the bowl of food and it's all over the counter, in the next scene, all the food has been cleaned up and is neatly back in the bowl. Not enough time had elapsed for the contents to have been cleaned then placed back into the bowl.
When John is trying to do chin-ups in Mr. Woodcock's gym class, the final two close-up shots of John has him gripping the bar so loosely that would not support his own weight let alone do any chin-ups.
When John slips off the treadmill, he smashes into the weightlifters. Yet when that happens, a few of them bend where John hits them.
At the Italian restaurant, when Woodcock is trying to remember Farley, he says "It's coming back to me" but his lips aren't moving.
When John arrives home at the airport in Nebraska, there are palm trees in the background.
A small Nebraska town will have almost zero swimming pools outside of a public pool or two. A private pool service would be a tough way to make a living (which is probably why he didn't have any clients).
Farley's agent calls him from a plane using a cell phone. It seems that the plane is in the air during this scene. Talking on a cell phone would be not be allowed during a flight.