This may be a controversial inclusion, but Charles Xavier has this nasty habit of taking over people's minds. He even made his lady friend Moira Taggart forget she even knew him, which seems a little invasive.
Will Smith's superhero with attitude is a drunk, anti-social guy with no respect for property damage or people's general well-being. He even stuck the head of one prison inmate up another inmate's rectum. That's not quite Boy Scout behavior.
This genetically-modified rodent has brains to spare and a sassy mouth, but he really gets his kicks gunning bad guys down and stealing people's prosthetic limbs for fun. He also stole valuable batteries from The Sovereign, kicking off a small war. Rocket may be a two-time galaxy saver, but he's got a thing or two to learn about personal property.
The Caped Crusader may have left a trail of bodies behind him in his quest for justice. Batman iced a few bad guys in the Tim Burton movies, but in Batman v Superman he straight up murders guys by blowing them away with Batmobile firearms or simply blowing them up with a grenade. It kinda doesn't even feel like self defense after awhile. In Christopher Nolan's The Dark Knight he also crossed a boundary by tapping into everyone in Gotham's cell phone in order to track down The Joker, which is shenanigans of Bush-ian levels.
Okay, let's just get this out of the way: Hit Girl is a murderer. She and her Big Daddy burn through bad guys in the Kick-Ass movies with guns, elbows, and anything else they have at their disposal. This is not good behavior for a child!
Joseph Dredd is an interesting example because he actually works within the system. It just so happens that the system he's under is a fascist future where cops have the power of judge, jury and executioner, with the punishment often not fitting the crime. Dredd hides behind a code of ethics, but it's a warped one, and it's interesting that many fans of the character don't pick up on this.
Short-order cook and religious nutbag Frank Darbo (Rainn Wilson) takes on the guise of The Crimson Bolt in James Gunn's 2010 satire Super. While the self-styled superhero vigilante deals out pipe wrench beatings to drug dealers and scumbags, he also beats a man for cutting in line at the movies. His partner Boltie (Ellen Page) is even more psychotic, killing several people with glee.
In his first two cinematic outings Frank Castle was essentially a Death Wish-style vigilante taking on criminals after the death of his family. By the time we get to Punisher: War Zone, he pretty much has no hesitation about turning bad guys into spaghetti sauce with guns, knives and anything he can find. No due process for this guy.
Wade Wilson was already a soldier of fortune who would give a guy a beatdown for cash, but after he was transformed into the unkillable mutant with a complexion problem we know and love... things got bloody. Wilson essentially goes on a massive killing spree taking on bad guys with no compunction about stabbing them, shooting them or rolling them over with a Zamboni.
Edward Blake (a.k.a. The Comedian) is like a bizarro world Captain America who smokes, drinks, rapes and kills at will. He's not afraid to put a rubber bullet in a hippie protester's back... or a real one through the head of JFK. He's as close to a hardcore villain as a hero gets.