[52:12]When Rick asks Gary for the key to his grandma's house in the stairwell at school, a dark haired guy in a light blue shirt walks down the stairs on the left side and cuts in front of them at the beginning of the scene. Right at the end of the scene, this same guy walks past them down the stairs again in the same direction.
[23:25]When Gary gives Karen a ride to school, as they pull into the parking lot you see 1 parking space available between 2 cars, 1 yellowish and 1 a blue/gray. After Gary parks, there is now an extra space between his car and the yellowish car and the blue/gray car has disappeared.
[1:00:41]When Gary, Rick and David are in the pool, the position of the Dr. Pepper can, the cigarettes and the blue towel change when Karen and Rose walk up. Also, the barely noticeable pack of matches sitting on top of the cigarette box disappears.
[30:12]At the party Gary stumbles drunkenly up to Karen and Rick who are kissing. When they separate Karen's lip gloss is freshly applied when it should be smeared all over her face.
When Karen is getting an abortion, Gary is told to pick her up at 6PM. When he arrives, the sun is seen shining through the windows onto her bed. Since this takes place over Christmas break, in December, the sun would have already set.
[6:21]When the guys bring home the girls they picked up at the restaurant at the beginning of the movie, Gary goes over to the stereo and places an album on the turntable. The song that starts playing is "In The Flesh" by Blondie off of their self titled debut album. The label on the record shown is not the label that would've been on that album for either record company that released it.
While the three boys are in the pool David mentions his back is badly sunburned since they were there for four hours, yet when they exit the pool David's back is pasty white. Given David's personality, this was most likely just him being a complainer.
[23:03]When Gary first meets Karen and gives her a ride to school, he asks her what her name is but he doesn't tell her his name and she never asks him. Right as they get out of the car and she declines his invitation to the party she says, "Thanks again, Gary." He could've told her his name during the drive to school. Just because we don't see it on camera doesn't mean it didn't happen.
[47:22]As Gary and the gang take off from the pizza lady's house you can see the camera lights as they reflect onto all the taillights reflectors on the parked cars (including) Gary's pizza wagon.
[1:06:40]There is someone walking underneath the bleacher on the scene where Rick and Karen go to do it while Gary pulls up in his car.
David tells Gary that Karen is new in town, just moved about 2 days ago. Yet, Karen is sitting at a table with many friends, including Rose. It's highly doubtful that a new student could make friends so quickly.