Continuity mistake: When the four guys are waiting for the second doll-woman to appear, Gary's hand jumps from sitting on his leg to being up by his chin.
Revealing mistake: When Gary and Wyatt come home and see Chet turned into a pile of poo, Chet shoots his tongue from his mouth and catches a fly. Look closely, the tongue flies completely out of his mouth and is attached to a metal spring.
Other mistake: In the mall scene, when Gary and Wyatt sit down on the bench and Max and Ian dump the Icee on them, notice how much slush is actually dumped on them from a 32 oz. cup.
Continuity mistake: When Gary grabs the FDX system unit (Memotech), the monitor (with green text) which sits atop the system unit falls backwards, and he then throws the system unit out the window. However, the FDX unit is back on the desk, with the monitor atop it (they are between the display monitor and feed scanner), when the boys are on the floor.
Continuity mistake: In the scene where Wyatt and Gary are taking Deb and Hilly home in the Ferrari and Porsche, Gary is being pursued by the police. When Gary approaches the railroad tracks, the train is shown coming in the direction of the passenger side door. When they finally cross over the tracks, the shot is flipped, and the train is seen to have crossed the intersection in the direction of the driver's side door.
Continuity mistake: In the gym, when Ian and Max walk up behind Gary and Wyatt, there is a closeup of their feet, and we see that the left laces on Gary's high tops are laced all the way up, tied snugly. However, when Ian and Max pull down the boys' shorts, in this close-up Gary's laces are only midway up the high top's eyelets, loose and untied.
Continuity mistake: When the ritual candles are first seen, one of them sits in a white corner area of the Life boxtop. In a later shot the candle moves in and sits on (newly appearing) black text.
Continuity mistake: There aren't any shoes on the Lisa doll, but the real life Lisa appears wearing high heels.
Other mistake: Garry and Wyatt are sitting on the side of a 'planter box prop' that was built for the movie, not a bench, when Ian and Max spill the Icee (slush) on them.
Continuity mistake: Lisa is trying to convince Gary's parents to let him go to the party. There is a glass of beer on the table. The camera switches to a close up and then back to a wide shot and the beer is gone.
Factual error: When Anthony Michael Hall is being pursued by the police, they have the logo of City of Los Angeles, but this takes place in Chicago.
Continuity mistake: When Lisa's confronting Gary's father, her hands rest on her hips as clenched fists. As Gary sits down after being told to shut up, Lisa's hand is open palmed.