During his time at Hogwarts School for Witchcraft and Wizardry, Harry and his friends developed a reputation for rule-breaking. The characters from Harry Potter are far from the only teenagers to push boundaries during their time at school, but the nature of their crimes was often more severe than average mischief.
There is a lot of trouble that someone can get into at a magical school, and Harry, his friends, and his enemies managed to find a way to check most of them off their lists. From ignoring basic boundaries, all the way to attempted murder, the breaking of rules varied greatly in severity for the students of Hogwarts.
Ignoring Any Direct Order
On the most basic level, Harry never took the orders of his elders very seriously. While he cared about a great many of his teachers, there wasn't a single one that he could be counted on to listen to 100 percent of the time.
While Snape's orders were guaranteed to be ignored, Harry was also known to ignore McGonagall and even Dumbledore's orders. If Harry was told to drop a mystery and focus only on his studies, there was no possible way that he would listen.
Cheating On Homework
Cheating on homework is another broken rule that any high school would be familiar with. For Harry and Ron, they were lucky enough to be best friends with the smartest student in the school.
Hermione often pretended to despise cheating, but when it came down to it, she couldn't handle the idea of letting Harry and Ron turn in poor work. She would offer to "fix" their essays, but more often than not she just completely rewrote them. Without Hermione's cheating, Harry and Ron might not have ever made it through some classes.
Talking Back To Teachers
Harry had a bit of a temper, and in the Harry Potter books, he could also be very sassy. If Harry disagreed with a teacher, he could not help but argue back. This was frequently seen with Professors like Snape, Umbridge, and even Lockhart.
Harry responded to these teachers with a large amount of sarcasm, and this gained him many detentions. However, his classmates credited these actions to heroism and looked up to him because of them. While this could sometimes be the case, other times, Harry was just being a snarky teenager.
Roaming The Castle At Night
One of the most heavily enforced but largely ignored rules at Hogwarts is that students are not to leave their dormitories at night. Once Harry got his invisibility cloak, however, there was very little stopping him from doing so.
Once or twice, Harry had some very close calls, especially when Peeves got involved. But overall, Harry got away with this crime. Dumbledore himself knew that Harry had this habit, but only seemed to care about it in Prisoner of Azkaban when he thought Sirius Black was after him (Harry ignored the instructions to stay in bed even then.)
Sneaking Into Hogsmeade Village
In Prisoner of Azkaban, Harry had been unable to get his Aunt and Uncle to sign a permission slip allowing him to go to the wizarding village of Hogsmeade on select weekends of the school year. So he had no choice but to watch his friends leave for the village without him.
With the help of Fred and George, and the surly highly illegal map that they gave him, Harry was able to sneak through hidden tunnels and go to Hogsmeade under his invisibility cloak. McGonagall had made it very clear that he could only go with a permission form, but Harry very didn't seem give this rule much care.
Blackmail
In Goblet of Fire Hermione was determined to discover how Rita Skeeter was discovering everyone's secrets. Over time, she was finally able to put the pieces together and she discovered that Skeeter was an unregistered animagus and could turn into a beetle.
Hermione managed to capture Rita in her beetle form and decided to hold her prisoner for a time. She also blackmailed the reporter telling her that if she wrote anything nasty about anyone, she would reveal her illegal means of getting the information. While Rita Skeeter had it coming, kidnapping and blackmailing are still pretty serious crimes.
Smuggling A Dragon Out Of The School
Hagrid was also no stranger to breaking Hogwarts rules (and the law) and unfortunately, he often brought Harry, Ron, and Hermione down with him.
In Sorcerer's Stone, Hagrid purchased an illegal dragon egg from a stranger but quickly realized after it hatched that he could not possibly keep it. In a Harry Potter book moment that should have been in the movie, he asked for the golden trio's help. Ron contacted his brother and arranged to meet him at the top of the astronomy tower, and Harry and Hermione carried it (Norbert) up at night while under the cloak, effectively breaking at least three Hogwarts rules and Wizarding laws.
Illegally Becoming Animagi
Harry got his talent for rule-breaking from his father, who also did a great deal of criminal activity during his time at school, which is why he is the Harry Potter character that most deserves a spin-off movie. In addition to creating the map that allows the user to keep tabs on anyone within the castle and identity secret passageways, James and his friends went through the complicated process of making themselves animgai.
Harry, Sirius, and Peter went through the effort so that they could spend time with Lupin while he was in his wolf form. It took them several years to be successful, but by their fifth year, they had achieved the tricky transfiguration.
Drugging Classmates
Once again, the most outrageous examples of rule-breaking were done by Hermione. In Chamber of Secrets, Hermione had to figure out how to get hold of Crabbe and Goyle's hair, as well as get them out of the way, so that Harry and Ron could use polyjuice potion to take their places and get information out of Malfoy.
To achieve this, she drugged and locked away the two 12-year-old boys, a crime that really could have led to expulsion. In her defense, Crabbe and Goyle were both fine after, and this scene gave an opportunity for a great performance from these young Harry Potter actors.
Attempting To Murder A Professor
Perhaps the worst crime, but also the most sympathetic, Malfoy once attempted to murder Dumbledore himself. In the attempt, two students were seriously injured and only survived death because of pure luck.
Malfoy never wanted to kill anyone, but fear for his own life, as well as the lives of his family, motivated him to try to achieve Voldemort's task. Had he been caught, Malfoy would have not only found himself expelled from school, but he likely would have ended up in Azkaban as well. Thankfully, Dumbledore understood the pressure he was under and did not hold it against him.