Continuity mistake: When Peter starts grabbing himself, his shirt is seen semi-tucked into his pants. The camera angle changes and the left side of his shirt is now hanging outside of his pants. (00:55:34)
Visible crew/equipment: When Peter is at the golf course with Mrs. Arness, you can see the golf cart behind them. In the next scene, there is a woman sitting in it and she appears to be the stand in for Mrs. Arness. (Confirmed on the audio commentary). (00:40:05)
Continuity mistake: Peter picks up Georgey, who is holding his Gameboy, spins him around and sits Georgey on the kitchen counter. In the next shot, the Gameboy is gone. It's not on the counter or in his pocket. (00:21:35)
Revealing mistake: When Mrs Arness and her dog, William Shakespeare, are at Peter's house, the dog walks over to Georgie. You can see the actor who plays Georgie had to hold dog treats in both of his hands to keep the dog near him in the scene. Confirmed in the audio commentary. (01:09:05)
Continuity mistake: When Queen Latifah comes in the house after talking to Widow, Steve Martin is sitting at the kitchen table. Watch his glasses move from the edge of the table to the stem of the wine glass and to various spots on the table throughout the scene.
Deliberate mistake: It is not believable that Charlene, the dangerous prison escapee, would seek legal assistance to re-open her case, and not be concerned about escape charges, in addition to freely being seen by many people.
Continuity mistake: At the end of the movie in the scene where they are moving into the new office, Peter is talking to Charlene at his desk. Behind her there are three books stacked in a certain order. Later in the scene when he is talking to his wife the books are stacked differently. (01:37:40 - 01:38:45)
Visible crew/equipment: When Peter is going home to get ready for his "date", he goes to get wine out of the fridge. If you slow down on the DVD you can see part of the camera and a man in a pink shirt standing next to the camera operator (director Adam Shankman?).
Audio problem: After Peter picks up Charlene, he drops her off at his house. As he's pulling up to his house they are having a conversation but you can see that their mouths are not moving. (01:20:31)
Revealing mistake: During the fight scene between Charlene and the girl, as Charlene hits the woman it is visible that she does not even touch her.
Continuity mistake: When Peter catches Georgey reading the adult magazine, Peter says to Charlene, "I'm turning you in." At this point in the movie Peter doesn't know she escaped, so there would be no reason to turn her in.
Continuity mistake: When Charlene's ex-boyfriend tells Peter to stay away from her, he holds a gun to Peter's cheek in the car. The camera angle changes and the gun is no longer pressed against his cheek. (01:18:06)
Continuity mistake: When Peter falls down with Charlene in the front yard, Peter is seen almost on top of Charlene but when the camera angle changes they are almost side by side.
Continuity mistake: When Steve Martin is trying on outfits before Charlene comes over, he puts a sweater on over a collared shirt. When he looks in the mirror, his collar is all messed up, but when he turns around, his collar is straight. (00:11:25)
Continuity mistake: After Charlene turns on the CD player she reaches over and grabs Peter's shirt by the second button. The camera angle changes and her hand is now seen at the middle of his shirt. (00:54:09)
Continuity mistake: After Peter and Charlene get back from dinner, Charlene turns on the CD player, lays the remote down, and turns around to face Peter. The camera angle changes and she is seen turning around again to face him. (00:54:02)
Continuity mistake: While at dinner with Charlene, Peter is seen getting ready to take a drink from his glass as Charlene asks him to dance. The camera angle changes and the glass is not near his mouth anymore. (00:50:43)
Continuity mistake: After Peter picks up his kids at his ex-wife's house, they are driving down the road talking and you can see a car right behind him as he drives. The camera angle changes and the car that was behind them is nowhere to be seen. (00:24:23)
Continuity mistake: When Steve Martin and Queen Latifa are dancing at the club that his ex wife and her sister are eating at, when the ex wife and sister are talking the ex wife's bangs change from sideswept to centre.
Other mistake: When Ashley is at the restaurant with Kate she looks in her mirror and sees Peter dancing with Charlene. This wouldn't be possible as she was on an upper level to the dance floor and she wasn't holding her mirror at a slant. (00:49:45)
Answer: It's called "Way of Life" by Lil' Wayne with Big Tymers and T.Q.