In the first opening cheer-leading scene, Jessica runs off to the side and says, "Ready, Hindenburg?". While the character's actual name is "Hildenburg", this is meant as a joke on her weight, in reference to the famous blimp, and is entirely intentional.
"Ling Ling" is a stereotypical Chinese name and does not come close to a Korean name. When Keesha's mother first appears in the movie, she is dressed in traditional Chinese clothing and not Korean. At the graduation scene at the end, however, Keesha is wearing correct Korean traditional dress.
The night before Jessica becomes a man, she is talking to April on the phone about how everything is perfect. Then she puts her phone down and goes to sleep, but it in the morning it is in her hand still though she clearly puts it down.
When Jake speaks to April after his skiing trip, he very obviously has love bites all over his neck, yet whilst changing after the football game only a few moments later, there is no sign of any of them.
When Clive is checking the oil in Jessica's VW, Jessica honks the horn while Clive is under the hood and the ignition is off. This is impossible on most German cars (and Volkswagens in particular), as the horn is disabled when the ignition is switched off.
At the end of the film when Clive is handcuffed inside the police car he opens the door and escapes. This is factually impossible since police cars do not have handles on the inside and can only be opened from the exterior doors.
While checking the oil on the VW Bug Clive Maxtone burns his arm, but there is no area hot enough for someone to burn themselves where his arm was. While checking the oil he pulls the dipstick out of the wrong place on the motor, too. On a VW Bug the dipstick is directly in the center-front of the engine.
When Jessica chokes Clive (while their bodies are still switched) Jessica later reveals she actually took the earring off of her ear, however when the strip club manager pulls him off when he was choking her we clearly see nothing in his hands.