Factual error: In the very first scene in the film when the magazine covers are flashing up, the very first one has a headline which says "loose that belly". For a film whose title has the word "lose" in it, you'd think that they could spell this properly.
Continuity mistake: When Andie brings the dog into Ben's office, Ben, Thayer and Tony are standing around listening to Ben complain about how Andie is driving him crazy. Tony is holding a white mug with black writing on it, and he hands Ben a plain black mug. Just as Andie walks in, the shot changes to her, then back to Ben and his friends. However, now Ben has a gray colored mug and Tony has a black one. (00:50:15)
Continuity mistake: NBA Finals-Game 1. Andie wants Ben to buy her a Coke. During this scene, the camera cuts back and forth between Andie and Ben, and the basketball game. When Ben first looks at the game clock there is a little over a minute left in the game. He rushes to get her soda, and when he gets back, she says she wanted Diet Coke. There is a shot in this sequence where the camera is filming the basketball action, and you can see the game clock with over 7 minutes remaining, even though they are supposed to be nearing the 30 second mark. (00:33:35)
Continuity mistake: In the scene where Ben is changing his shirt in his office, and the women outside are watching him, when he puts a new shirt on, the left side of the collar is tucked into the inside of the shirt. The camera cuts to a side angle, and the collar has mysteriously corrected itself. (00:06:49)
Continuity mistake: In the scene where Andie is trying to get Ben to look at the photo album and Andie starts to cry, Ben covers his mouth with his fist. In Andie's close up, you can see that Ben has his hand beside his beer bottle. When it shows a close up of Ben again, his fist is still on his mouth.
Continuity mistake: When Ben walks into his office, just before he says, "What's up kitty cat?" in this shot in the background the woman with a black sleeveless top is leaning over a desk speaking with someone. In the next shot as Ben asks, "Where were you man?" that woman is standing by the coffee machine at the wall at the right. Yet, in the next shot, she's back where she was in the first shot. (00:05:45)
Continuity mistake: During the Knicks game, there is a shot of the scoreboard with about one minute left. The main score says that the Knicks have 93 points. However, if one adds up the player-point totals on the left (42, 9, 21, 14, 8), the Knicks supposedly have 94 points.
Continuity mistake: When Andie first goes back to Ben's apartment and they kiss by the mirror, she is suddenly wearing rings on her wedding finger, when previously she only had rings on her right hand middle finger (these are still present as well). These then disappear again when they reach the bed. They then make another appearance in the scene in her friend's flat when she has the cat on her lap. (00:26:24)
Continuity mistake: In the scene where Ben and Andie are in the bathroom together, after they have been splashed by the truck outside, Ben's shirt is almost dry and only a faint line of wetness is visible. In the next shot of them in the bathroom, his shirt looks as if has been just drenched a few seconds before. (01:20:12)
Continuity mistake: Towards the end of the movie when Michelle and Andie are watching the Final Game at Michelle's apartment, the doorbell rings. Michelle assumes it is the Chinese food they have ordered. As she walks to the door she picks up her wallet. When she answers the door and realizes it is not Chinese food but Mike, she slams the door and puts her wallet back down on the table. Before she re-opens the door to talk to Mike she has her wallet back in her hand and puts it back on the table, again.
Continuity mistake: When Andie walks in and surprises Ben at work, Ben shouts, "Andie!" and he places his light mug down and then it is seen next to the side pocket on the pool table. In the close-up of the dog on the pool table, the light mug is closer to the corner pocket, with the black mug. (00:50:20)
Continuity mistake: At his office, when Ben starts removing his tee shirt, three women, holding their coffee mugs, are huddled together glaring at him in two shots. After he flicks the ad with his fingers, two of those women are walking around at the other end of the office, doing their work. Yet when Ben says, "No way!" he turns and sees the three women, still huddled together holding their coffee mugs, glaring at his body. (00:06:10)
Plot hole: The scene where Andie comes over for dinner and moves a bunch of frilly stuff into the bathroom, happens at least one day before she comes over with the wedding album she made. In that scene, Ben goes into the bathroom to splash water on his face and discovers the pink hand towel and other stuff - that means he would not have gone into his bathroom for at least a day, or two, since she put the stuff in there, or he would have noticed it sooner.