Character mistake: Near the end, just before Derek and Danny depart at Danny's high school, Derek says to his brother "I saw a car cruising by the house last night when I pulled out of there with Seth." The car that was shown driving by their house the previous night was in a brief scene right after Derek and Danny took down all of their nazi posters, and before Derek took a shower. He had not just 'pulled out of there with Seth.' The last time he had seen Seth at this point in the movie was at Cameron's party where Seth had almost shot him.
Suggested correction: Just because Derek says to Danny that he saw a car driving by their house when he left with Seth and a black car drove by later in the movie doesn't mean that this is the car Derek was referring to. There are many possibilities to explain what Derek was referring to (perhaps he was paranoid and saw an ordinary car driving by that he thought was scoping their apartment out) but it doesn't mean that the black car is the one he was referring to when he warned Danny.