Continuity mistake: When Mike is trying to get Mark to ask Stacey out, there is a shot of her behind the counter and Stacey's hair is pulled back on the sides in french braids with ribbons on the ends. Then when Mark approaches Stacey, her hair is pulled back in a clip. The first shot of Stacey with the braid, is actually cut from a scene later in the film, when Mark and Stacey talk at the counter.
Continuity mistake: After the Last Dance scene, they show a night shot again like in the very beginning of the movie of people coming and going at the mall. If you look closely, you can tell this was shot the same night the beginning scene was filmed. For instance, the guy in the grey blazer and black pants is there again, but what gives it away most is the woman on the far left in the red and white Hawaiian dress, she even is in her same spot as the scene at the start.
Continuity mistake: When the Santa sits down in the Pizza place after getting urinated on, when his food is brought over his fake mustache is covering his mouth because it's so big, then a second later when he is shown again, the mustache is suddenly smaller and you can see his mouth.
Continuity mistake: When Brad admits to his boss he threatened his customer, Brad is shown and there's nothing out the window behind him. Brad is told he's fired (instantly) and then Brad's shown again (only one second later from same exact position) with a potato chip truck sitting still out the same window. There's no way a truck could just appear out of nowhere in only one second-slowing down to a stop maybe, but not sitting still that quickly.