Continuity mistake: In the scene when the Sherminator is talking with Matt after returning from band camp, Matt is wearing a purple shirt. But when Matt asks if "everyone hated his brother", in the reflection of the star trophy on the desk, you can see Matt's reflection, and he is wearing the orange and black striped shirt from the earlier scene where the Sherminator sends him to band camp. Clearly the two scenes were cut together.
Continuity mistake: Towards the middle of the film, Matt is doused with water from a girl he's trying to hit on. The water pattern changes between shots on his shirt. In one scene his right shoulder and part of his chest is wet; then his entire shirt is wet; then back to the shoulder being wet.