Complete Monster: Clarence Darby rapes Clyde Shelton's wife, murders her, savagely beats Clyde with a baseball bat, and then murders Clyde's young daughter. They don't even show the audience that scene; it's so horrible. He just takes her into the next room. The line "Don't worry...kids like me." could hint that he raped the girl too. He also attempts to murder Clyde. He proceeds to lie, saying that his partner did it (when, in fact, the partner had tried to talk him out of it), and subsequently laughed his head off when he hears about his partner's agonizing death.
Darkness-Induced Audience Apathy: This feeling hits home for viewers who become increasingly disillusioned with Clyde's actions halfway through the film. Clyde starts off as sympathetic, but he eventually becomes worse than the madman (Darby) who sparked off his rage in the first place. As for the attorneys and lawyers on the other side, they're immoral strawmen made to look as corrupt as possible, except for Sarah, who dies thanks to Clyde. When one realizes Clyde's hypocrisy reaches the level of Jigsaw it's impossible to root for anybody. See Black and Gray Morality.
Also, Nick's response to his partner asking about Clyde's civil rights? "Fuck his civil rights." It's supposed to come off as awesome, but that's a reallybad ideology.
Draco in Leather Pants: There are quite a few people who present Clyde as a hero fighting a corrupt system, ignoring that many of the people who die at Clyde's hands were simply employees doing their jobs and not actively trying to wrong him. That and he killed his cellmate simply to advance his plot. Clyde might be sympathetic, but the crimes he committed are still wrong.
Faux Symbolism: The fires that surround Clyde the last moment we see him in the film before his death.
When Sarah and the others are blown up outside the prison, Clyde is shown in priest-like black clothes and white undershirt, fingering his daughter's bracelet which resembles rosary beads.
Hilarious in Hindsight: At one point Bray says "spies are a dime a dozen", which was included in the trailer. This unintentionally mirrored a line from Team Fortress 2's trailer "Meet The Spy", which has the Scout saying "[Spies are] dime-a-dozen back-stabbing scumbags!" The payoff? Well, see Law Abiding Engineer.
Jerkass Woobie: Clyde, he kills a lot of people, but he had his wife and daughter murdered and the main perpetrator got off with a slap on the wrist.
Ames could also count. Yeah, he was Darby's accomplice, but he only wanted to rob the place, he didn't want to kill anyone. Darby sold him up the river when he tried to stop him. Just before his execution, he says that he regrets ever having been there that night. The fact he died a horrible death is pretty sad.
Magnificent Bastard: Clyde Shelton. You may not approve of the idea that guides him, but you have to admit and admire his style and execution.
Initially, we can sympathize with Clyde Shelton's desire to kill Clarence Darby as vengeance for killing his wife and kids. But then there's how he goes about it: paralyzing his body, taking him to his lab and chopping of his limbs with a chainsaw, making a video of this, and sending the video to Nick Rice.
Though some would argue that a monster like Darby was simply getting the kind of punishment he deserves. Gruesome fate for a gruesome individual.
He definitely crosses it when he murders his cellmate for no other reason then to advance The Plan. Although there are many different views, this is the most widely cited.
And for those who think that all of Clyde's victims were Asshole Victims in some way or form, the final straw is when Sarah becomes one.
Rooting for the Empire: Deconstructed. At the beginning one is hardfelt to not be rooting for Shelton's Roaring Rampage of Revenge against the people that wronged him and the system that deliberately let his killer go just to keep up appearances. But it slowly changes when it becomes clear of how vast Shelton believes the people involved are and is ready to kill a lot of innocent people just to get his revenge.
They Wasted a Perfectly Good Plot: For most of the movie, we are led to believe that Clyde is getting away with his crimes because he has someone helping him on the inside. When we find out that he has no help, and that he has a tunnel system that takes him from his solitary confinement cell to wherever he wants to go to carry out his crimes and back again before anyone notices, many thought him having a partner was better and made more sense, and this twist broke many a suspension of disbelief. If ANYONE checked up on him while he was out committing his crimes, he would have been exposed, plus it means he carried out highly elaborate and sophisticated murders, many of which required precision timing and a level of improvisation, entirely by himself, when again a partner would have been more plausible.
Unfortunate Implications: The line "Fuck his civil rights" can really rub people the wrong way and give them the wrong impression, as it more or less implies the law is pretty corrupt and will throw ordinary people to the wolves if need be, as one review points out:
"But if Law Abiding Citizen wants to be a story about an ordinary man — Shelton — who takes back a power he believes has been given up to those in charge — Rice — a power those in charge have abused, why is it ultimately espousing a route that would do nothing but give those in authority even more power over ordinary people? If Shelton’s civil rights are fucked, then so are yours and mine."