Accidental Aesop: The most straightforward aesop is the dangers of racism, though it can also be viewed as the dangers of idolization towards individuals (including family members and their beliefs) without thinking, ranging from Derek's dismissal of his black teacher's lesson from his father's lecture to Henry's murdering Daniel due to influence of his elder brother as example of its message.
Crosses the Line Twice: Seth's white supremacist rendition of The Battle Hymn of the Republic. The lyrics are hateful and racist, but Seth's exuberance while singing makes it uncomfortably amusing. Even worse, that's an actual song by Johnny Rebel.
Do Not Do This Cool Thing: The film's message is "racism is bad", but the contrast between the generally charismatic Nazis and the villainous black gangs, along with some general Misaimed Fandom tendencies among certain audiences, and the fact Danny is ultimately killed by a black guy, means that the film is actually quite popular in certain white supremacist circles. It might have been even worse if they had kept the original ending, where Derek goes back to being a Neo-Nazi after his brother's murder.
Harsher in Hindsight: The ending where Danny gets shot in the school bathroom becomes this after Columbine happened a year later. Adding to it was the rumors that the shooters were Neo-Nazis because they chose to do the shooting on Hitler's birthday.
Derek himself. He turned into a vicious thug, but that was only after his father was killed putting out a fire.
Misaimed Fandom: In spite of the film's anti-racist message, it still has a large number of Neo-Nazi fans due to the fact that Derek is strong, charismatic, and a natural leader. It doesn't help that he's photographed like a badass athlete in a basketball commercial. See Do Not Do This Cool Thing.
Derek's fellow members, especially Seth and his girlfriend, threatened to shoot him when he decided that he was through with the neonazi life.
Cameron was obviously beyond it, what with being behind organised attacks against immigrants but he also said he that Danny would take Derek's place and Derek wouldn't be able to get away from it.
The prison rape as well though it is hardly surprising from such scumbags.
Henry shot Danny to death. While Danny was a Neonazi the only thing he did to him, was defy him while he was bullying another student for no good reason. The biggest culprit was his brother who told him to do it as his initiation into their gang.
Signature Scene: The curb scene. If the name of the movie doesn't ring any bells to someone, it will after you remind them of this scene.
There is still a shockingly high number of Neo-Nazis both in California and Tony Kaye's native England. There's no other way to say it, either; racism is a pointlessly destructive thing no matter who its perpetrators or targets are.
In addition, it also showed the role of Big Brother Worship, Hero-Worshipper, and family structure in continuation of destructive beliefs (such as Derek's gang and their black rivals, Danny's eventual turn to Neo-Nazism, and Danny's murderer being influenced by elder members of family) and basically telling the audience to think before blindly following what they think of as a paragon to their life. Along with trying to learn more from other side on their judgement (Derek's discussion with Lamont, who helped him remind of Dr. Sweeney's lesson).
Squick: Derek curb-stomping the black guy to death.
Values Resonance: With stories of police brutality coming out everyday, this movie is even more relevant in the dialogue on racism.