Visible crew/equipment: Before the start of the last basketball game, when Ned calls out, "Jane!" for the third time in the shot facing him as he tries to pass someone, the actors' green T-mark and three other tape marks - one yellow and two red - are visible on the floor ahead of Ned. (Visible on DVD fullscreen.)
Factual error: At the start in 1989, when Mike is dancing with the cheerleaders and also just before he goes after Scarlet, in close-ups of the crowd cheering there is a man (with a white baseball cap) wearing a Paramore t-shirt. However, Paramore (a Grammy-nominated American pop rock band) formed in 2004. The style of t-shirt he is wearing is actually one of the officially licensed Paramore merchandise.
Continuity mistake: When Mike walks into Health class, Mrs. Dell's lectern and stool (upon which the basket of condoms and another basket sit) stand directly in front of the chalkboard, but funny how they are both conveniently gone when Mike knocks Stan to the floor, in front of that chalkboard.
Continuity mistake: In the shot just after "Mark" tells Scarlet about Alex and the new girlfriend, Nicole (at the victory party), we see Jane's car driving down the block (towards the camera) headed to Ned's home and there are multiple black tire tracks (burned rubber) on the road at the intersection. After a close-up of Jane and Ned in the car discussing 'Halo', it cuts back to the intersection as the teenagers cut them off, and the tire tracks are gone.
Visible crew/equipment: In the opening shot of Ned and Mike in the kitchen, with frozen veggie ice-packs on their assorted injuries, just before it cuts to Ned staring at Mike, the actor's orange tape mark is visible under his feet as he is sitting on the stool. (Visible on DVD fullscreen.)
Visible crew/equipment: When Mike satiates his hunger in Ned's kitchen, just after Ned says, "That's your can now, we'll label it like that," the reflection of a crewmember moving around is visible in the cabinet's glass pane, to the left of the screen. In the other shots of the same angle we don't see movement, so we know it's not Mike's reflection.
Continuity mistake: Before the '89 basketball game begins, Mike is on the court with the cheerleaders and when he pulls off his blue snap warm-up pants he is wearing the grey uniform shorts and jersey. However, after Mike poses in the close-up, he is wearing the blue warm-up pants again in the next shot from behind the cheerleaders - note his jersey number "0", which is visible between the cheerleaders.
Continuity mistake: On the bridge, when Mike topples into the water headfirst, the distinctive treads on the heels/soles of his shoes, as well as the light colored brand logo on the heels, are visible. After the newly transformed Mike appears at Ned's home wearing the same clothing, when Ned pulls the rug out from under Mike, his shoes' soles are completely different.
Continuity mistake: The morning after Mike's party at Ned's house, when Ned finishes vacuuming the rug in the overhead shot the wood floor immediately surrounding the rug is clean, but in the next shot there is a mess right beside the rug, which would have been visible in the previous shot had it been there.
Continuity mistake: At the restaurant, after Ned does his wine tasting, when the waiter pours wine into Jane's glass he holds the bottle in his left hand, as his right hand holds the cloth napkin, then lifts the bottle away from the glass when he is done. Next shot as he still pours wine in Jane's glass, the wine bottle is now in his right hand as he holds the base of the bottle with his left hand.
Continuity mistake: During Mike's first class (before Maggie walks in), when he's on the cell with Scarlet, who is asking where he is, a cheerleader sits down behind Mike and places her right arm up with her hand at her chin and her left arm is down. However, in the next shot when she asks Mike if he would consider a 10th grader, now it's her left arm that is up and her right arm is down, instantly.
Continuity mistake: When Mike swings his lightsabre and causes Ned to slam backwards onto the floor, Ned drops his own lightsabre onto the floor beside him, with its red glow pointing toward the front door. Next shot the lightsabre is turned the opposite way, with its red glow pointing toward the kitchen.
Continuity mistake: When Mike grabs a lightsabre and shouts, "Ned, Ned, Ned, I'm telling you...stop it!...Now!" his arms are extended out with the lightsabre held aloft, and his tie hangs properly. It cuts to Ned turning on his lightsabre's glow effect, with Mike and his raised lightsabre in the foreground. In the next shot, as Mike's arms are still extended out, his tie is now dangling over his right arm.