In the make-out scene when Rick & Karen are messing around in the backseat & Gary & Rose in the front seat, it is night but when the car goes into the ocean, it's sunset!
There's an outside shot of the parking lot of the hang-out & Gary's car isn't there. But when he storms out after finding out that Rick slept with Karen, the car is in the parking lot!
The car is there when he goes in. All the way to the left. Then there's a blue Corvette or sports car of some sort and then Karen's moped.
All throughout the film, Gary drives a pink station wagon, but when he pulls up to the football field, it's light blue! It even changes to light green on the highway after he's driven off after hearing that Rick slept with Karen. My speculation is that Larry Monoson was driving the pink car most of the time (that is, for the easy driving maneuvers because he was just learning how to drive) while the stunt drivers used the blue & green cars for riskier driving (e.g. driving on a busy highway & speeding & coming to a fast halt).
When Gary looks for Karen, it's night but then they cut to Rick & Karen walking along the bleachers & it's early evening. When they're in the dugout doing the deed it goes from evening to afternoon! The same thing happens when Gary is looking for them under the bleachers!
When Rick is having sex with Carmela you can tell that it's totally fake. The filmmakers try to hide it by shooting through the key hole and only showing half their bodies but at one point it you can see that Rick is lower than carmela.
Also, Carmela is voiced over when shes talking during it because her voice doesn't match her mouth.
In the 'Last American Virgin,' there's the scene where David is about to score with the blonde chick, but winds up crawling into bed with Gary's Mom. When David is with the blonde chick, they are sitting atop a king size bed. When David crawls into the bed with Gary's Mom in the dark, it clearly is a twin sized bed, not king sized!