Deliberate mistake: At one point they use a Red Ryder BB gun (Yes, just like in A Christmas Story) and the guy says "You pumped it more than twice, didn't you" to his female counterpart when they shoot the bird. Red Ryder BB guns cannot be cocked/pumped more than once, due to the simple nature of the toy gun that it is.
Continuity mistake: When Tripp has gotten ready for the day he comes down to the kitchen. We find his mother writing Tortilla Chips on the dry erase board. When Tripp finishes off the OJ in the kitchen he tosses it into the trash can opened by his mother. We see the dry erase board in a couple of different shots and the way it is written changes from shot to shot.
Continuity mistake: In the scene where Matthew McConaughey makes dinner to confront his parents and Sarah Jessica Parker about scheming to get him to move out his wine glass is magical. Before revealing he knows what is going on McConaughey stands up and drinks all of the wine in his glass and sets it back on the table. Seconds later, the wine glass has been magically refilled. And during his speech his wine glass jumps magically into his left hand before mysteriously returning to the table.
Continuity mistake: When Kit and Paula are drinking champagne, the way Kit hold the fluted glass continually changes between shots. First it is in the middle of the glass, then near the top of the glass then back in the middle. As they sit down her grip is way down at the stem of the glass.
Continuity mistake: When Paula is meeting with Mom and Dad, Dad asks about sex. At the end of her discussion about sex Mom exhales deeply. The lemon in her tea is standing up on end on top of the ice in her glass. The next shot is from over mom's shoulder and the lemon is now laying sideways in the tea.
Continuity mistake: In the final scene on the sailboat, Paula comes about (turns) at speed, and knocks Tripp off the boat when the wind swings the boom and mainsail across the boat. Paula releases the rope holding the mainsail up, dropping the mizzen sail, presumably to stop (or at least slow) the boat so she can help Tripp. When the camera pulls back as Tripp swims back to the boat, the mizzen sail is mysteriously up again. All of this occurs with Paula standing at the side of the boat, and no one controlling the wheel, and somehow the full sails never move the boat while Tripp is in the water.
Continuity mistake: Early in the film, Paula comes home and her room-mate, Kit, is there with a freshly poured glass of champagne. Kit says, "Hey, Paula, good news - it's champagne Thursday!" and pours a glass for Paula too. Throughout the scene, Kit's glass magically goes through various degrees of empty/full without refilling. Specifically, after Paula says she met a guy, and then sighs, the glass is much fuller, even though Kit takes a big drink. You can see this really well right when Kit says "How cute?"