When Hesher is thrashing around in the pool reenacting a scene from Star Wars, he yells "R2! Shut down all the trash compactors on the detention level!". However, in the original Star Wars movie, Luke is talking to C-3PO on the comm unit, and is yelling "3PO", not "R2".
The cuts on TJ's face from the wrecking yard are on his left side when he falls and leaves, but he has them on his left side and they're already done scabbing and look like scars when Nicole (Natalie Portman) shows up at TJ's house the next day to apologize.
After a fender-bender, Nicole is unable to start her car. We can see that her front bumper is detached and one side is resting on the street. So Hesher gives her a ride. But after she walks back to her car, it starts and runs with no problems.