Professor McGonagall appears to be as tightly wound as her signature bun hairstyle. Her stern demeanor strikes fear in the hearts of every Hogwarts student, from the grass-green first years to the seasoned seventh years. To McGonagall, tardiness, mischief, and rule-breaking are on egregious par with the Unforgivable Curses. Try any monkey business in her class and... well, you don't want to know what happens to the monkey.
That being said, McGonagall isn't some mindless follower of authority. She's one of Harry Potter's smartest characters. When power is being abused, McGonagall will stand up, wand at the ready, and fight for the good she believes in. Maybe that makes her a bad example to her students...or quite possibly the best role model ever. Here is Harry Potter: 10 Times McGonagall Should Have Been Fired (Or Imprisoned In Azkaban).
Favoritism runs rampant at Hogwarts. Dumbledore and Snape are the guiltiest of that. But McGonagall's firm but fair persona would make it seem that she's above such behavior. As head of Gryffindor, McGonagall certainly has no qualms about docking points from her house.
However, McGonagall has a weakness for Quidditch. She's downright desperate for Gryffindor to win the Quidditch Cup. So when she sees first year Harry performing death-defying stunts on his broom, instead of punishing him, McGonagall offers him a spot on the Quidditch team. Traditionally, first years aren't allowed on the house teams, so she's definitely bending the rules. Given Harry's talent, it's easy to see an exception should be made. But then McGonagall goes a broom too far and procures Harry a Nimbus 2000, a top-of-the-line broomstick. It's a sweet gesture, but downright inappropriate. If the Aurors were to launch an investigation called Operation Hogwarts: Varsity Blues, McGonagall would have a lot to answer for.
It's shocking how few Hogwarts professors take their students' safety to heart. In contrast, students know they'll always be safe within the four walls of McGonagall's Transfiguration classroom. But in the matter of assigning detention, McGonagall throws that caution aside like a broken wand. The miscreants' assignment is to go into the Forbidden Forest with Hagrid to search for an injured unicorn. What could possibly go wrong?
Yes, this is the same Forbidden Forest students were warned not to enter... unless they wish to die a most painful death. What a perfect spot for detention. Is McGonagall trying to play Russian Roulette with students' lives? No. She knows it's a pretty safe bet that all will be well. And unconventional punishments are effective. But considering what does happen, which is Harry and Malfoy coming face to face with a weakened Voldemort, McGonagall might want to reconsider her disciplinary methods.
In every academic institution, there's a hierarchy of subjects. At Hogwarts, classes like Transfiguration are considered fundamental and important, whereas Divination is a bird course. While this is the unspoken belief of many, it's quite unprofessional for McGonagall to insinuate as much in front of her students.
She's not trying to be a jerk. After Trelawney predicts Harry's death, there's a pall cast over the Gryffindor students. McGonagall's just trying to assure Harry he's not going to die. Morally speaking, she made the right call. But you don't have to be a Seer to know that questioning another professor's ability to do her job in front of other students could get McGonagall into some hot water.
This in and of itself isn't a crime. McGonagall went through all the bureaucratic red tape and signed off on giving Hermione a Time-Turner so she could attend more classes. However, when Buckbeak and Sirius' lives are in the balance, Hermione illegally uses the Time-Turner to go back in time and save them.
Should she have been caught, Hermione would have faced stiff punishment, and McGonagall would likely be in even bigger trouble as the authority figure who vouched for her. Messing with time is a serious infraction in the magical community, no matter how noble intentions may be. McGonagall should have instead advised Hermione to not spread herself too thin. Ah, well. Next time.
McGonagall's rebellious temperament is fairly dormant throughout the series. However, it's awakened full-force when a corrupt dictator rises to power in the form of Dolores Umbridge. McGonagall recognizes Umbridge as the Ministry for Magic sycophant that she is. Most of McGonagall's defiance is quiet and under-the-radar. Fans will never forget when she discreetly tells Peeves how to loosen a chandelier—with Umbridge as his likely target.
But McGonagall also openly shows her disdain for Umbridge. During Umbridge's assessment of Transfiguration, McGonagall straight-up calls her out for interrupting the class. After Umbridge sacks Trelawney, McGonagall comforts her. She's a smart cookie. She conducts herself just below the line of belligerence needed for Umbridge to fire her. Speaking of cookies, or biscuits, McGonagall offers one to Harry after he calls Umbridge a liar. Only McGonagall could be described as a badass with biscuit.
Under her reign of terror, Umbridge does her best to eliminate all threats, aka Dumbledore supporters. She enlists a band of Aurors to arrest Hagrid in the middle of the night, with the hopes of not causing a scene. What is she, new? Nothing gets past McGonagall. She leaps into the fray, demanding they leave Hagrid alone.
As Aurors are Ministry employees and have license to arrest people, McGonagall's actions constitute obstruction of justice. But instead of threatening her with such, the dirty Aurors hit her with four Stunner spells. While that's preferable to being thrown into Azkaban, it definitely qualifies as a cheap shot. McGonagall, boss that she is, survives—thankfully without an Azkaban sentence.
When Voldemort rises to power, any actions against him are punishable by Unforgivable Curse. But does Snakeface really think that'll stop McGonagall? As a member of the Order of the Phoenix, McGonagall is instrumental in helping Harry and friends break into Hogwarts for the impending battle.
The Carrows, Voldemort lackeys and Deputy Headmaster and Headmistress, interrupt. After a year of being under their thumb, McGonagall insults their intelligence with her signature dry wit. This earns her a loogie in the face, but she's still able to ensnare both Carrows in a net. This draws a line in the sand. Should McGonagall's side lose to Voldemort, Azkaban will look like a day spa compared to what the Dark Lord has in store for his detractors.
Death Eaters are like potato chips—bet you can't incapacitate just one. As Headmaster, Snape is her boss, but McGonagall's days of deference died with Dumbledore. Snape attacks first, but McGonagall attacks harder. A duel between the former colleagues ensues, and nobody pulls any punches. McGonagall conjures up fire and daggers, all aimed at Snape, all narrowly missing him. Aided by fellow professors Sprout and Flitwick, McGonagall forces Snape to flee the premises. It's a good thing the Battle of Hogwarts shakes out the way it does. In any other circumstance, McGonagall would have been so fired.
Instructing students in your care to commit an act of domestic terrorism is not something Minerva McGonagall takes lightly. But these are dark times, readers, dark times. The Battle of Hogwarts has begun. First order of business: the bridge needs to be destroyed to prevent any more of Voldemort's cronies gaining entry.
Even in these drastic circumstances, it's hard for Neville to wrap his head around McGonagall's orders. He double-checks, and McGonagall's response is classic: "BOOM!" Neville and company do as they're told, resulting in several human deaths. While McGonagall is no cold-blooded killer, she'll do anything to protect Hogwarts—even blowing it to smithereens.
At this point, McGonagall has completely broken bad, all in the name of Team Good. She enlists the whole school in fighting against Lord Voldemort. No, this doesn't just mean the students. Every object capable of being magicked into a solider or a weapon gets the McGonagall treatment. Suits of armor and statues come alive, ready for battle. Even desks find themselves flung at Death Eaters stupid enough to get in the way. McGonagall makes it perfectly clear—if Hogwarts is going down, she's going down with it. But never without a fight. McGonagall may be no-nonsense, but there's no doubt about it—she's a take no prisoners, rule-breaking Gryffindor right to the core.