Continuity mistake: In the confrontation scene where all of Mary's admirers are forcing her to choose between them, Woogie is sat on the couch with a pile of Mary's shoes. Every time the camera shoots back to him, you will notice that the position of the shoes changes each time. This is also mentioned by the directors on the DVD commentary.
Continuity mistake: When Ben Stiller got his "frank and beans" caught in the zipper, the friendly police officer thought he would assist with the problem. He unbuttoned his sleeves and rolled them up, but then the next camera shot showed them buttoned up, and had to be rolled up again. (00:17:30)
Continuity mistake: This is during the scene on the outside steps of Mary's office, when Mary and Ted see each other for the first time. A suit-wearing businessman comes from the left side of the screen behind Mary twice. This happens when Mary is saying "Ted? Is...Is that you?" and the camera goes back and forth between Ted and Mary. (01:11:30)
Continuity mistake: About one hour into this movie, when Healy is playing tag with the 'Neary group people' he goes for the touch down and Warren runs after him to get the ball. As Warren first dives for the ball, you can see that he has three red tags attached to his back, in the next shot as he lands you can see that the tags have disappeared. (01:09:10)
Continuity mistake: When Pat is spying on Mary, the first morning he spies on her, Mary leaves her house and walks down to a deck and she throws Herb an apple. In a wide shot, on the barrel next to Herb is a cup, yet in the following closeup a bottle of whisky appears from nowhere. (00:25:50)
Continuity mistake: When Puffy the dog goes crazy, he bites Ted's neck and Ted crashes onto the counter, smashing into some wine glasses and cups. Between a closeup and a wideshot, the smashed glass that lays around Ted changes. Also in the closeup Ted is fully on the counter, yet in the wideshot he is half on the counter, with his legs hanging off of the side. (01:29:00)
Continuity mistake: When we see the first shot of the meeting Dom is holding, you can see the meeting table with loads of sheets on it. Then it changes to a shot of Dom standing by his big pad (just before Ted runs and yells "Mary's a fox!"), and the sheets on the table have moved around and some have vanished. (00:41:45)
Continuity mistake: When Pat is round Mary's, he is holding the dog. Between a wideshot and closeup, the way he holds the dog changes. (00:44:40)
Continuity mistake: When Ted is laying in bed, he gets up and pushes his blue and red sleeping bags further down the bed, just before taking his picture of Mary out of his wallet. Between shots the position of the sleeping bags changes greatly. (00:33:05 - 00:33:35)
Continuity mistake: There is a scene where Ted and Mary are on a date and Mary is eating corn dog. There is a cut from her holding the corn dog where she and Ted talk and she doesn't eat any of it at all. Next shot showing the corn dog however, and there is a lot less than there was a couple of seconds before.
Continuity mistake: When Mary says to Ted "I have a lot of fun with him" about Warren, her hair falls over her eye. In the next shot it is pushed back. (00:07:20)
Continuity mistake: In the scene where Ted is sitting on his bed, he pulls out his wallet to look at a picture of Mary. When he first pulls it out, he is looking at it from the side. But when they actually show you the face of the picture, it is upright.
Continuity mistake: The crowd that watches the guy fight with Warren and Ted near the beginning keeps on changing. People move where they're standing between shots and the arrangment of the crowd changes throughout the scene between shots too. (00:05:15 - 00:06:10)
Continuity mistake: When the dog is dead, Pat tries to revive it by using some wires. When it fails, he puts the wires on the couch then peeks into the kitchen to see what Mary and Magda are up to. Then in the next closeup of the dog, the wires how moved to laying on his stomach. (00:46:15)
Continuity mistake: When Ted and Mary are sitting on top of the car, Mary looks at her watch to see what the time is, but if you look closely, her watch is facing the camera, so there is no way she could have seen what the time was. (01:30:35)
Continuity mistake: When the dog is on fire, Pat gets a vase of water and pours it on the dog. In a wide shot the dog is on it's back, with all fours pointed up in the air. Yet in the closeup of the water being poured on the dog, the dog is on it's stomach just sitting down properly. This is obviously due to the switch of the fake dog to the real dog. (00:46:30)
Continuity mistake: Ben Stiller gets "hooked" with Warren's fishing line, getting a hook that quite noticeably has the prongs sticking out of his cheek when they are removing it. In the next scene, however, no scar, and no sign of the injury exists. (01:36:10)
Continuity mistake: Tucker shows his ID bending its left side in the wide angles, yet in the close-up it appears straight.
Continuity mistake: When Ted sees Mary for the first time in years, the hood on his sweatshirt changes from his back to his right shoulder. (01:12:10)
Continuity mistake: When Mary has lunch with three friends, in a wide shot one of her friends picks up her drink and brings it to face level. In the following closeup of her, she brings the drink to her face again. (00:28:40)
Answer: Because he is ignorant and doesn't know anything about disabled people, he actually doesn't realise what he is saying is offensive.