In the world-famous "Harry Potter" series, the character of Snape was literally the worst. People use his difficult past and the fact that he spied for Dumbledore to justify his terrible actions, but he really was quite awful, and here's why:
1. Snape intended to kill a student's pet.
In "The Prisoner of Azkaban" Snape planned to test Neville's faulty Shrinking Solution out on his toad Trevor. He blatantly threatened to kill Trevor if Neville got the potion wrong: "If, as I don't doubt, he has done it wrong, his toad is likely to be poisoned." When Hermione helped Neville right the potion, Snape punished him because Trevor didn't die.
2. Neville's boggart was Snape.
Neville Longbottom knew tragedy from an early age. His parents were literally tortured to insanity, but survived physically. He visits them often and is reminded of their absence from his life. However, the thing that Neville fears more than anything is Professor Snape. His boggart took the form of Snape, and few people saw the problem with that.
3. He made fun of Hermione's appearance.
Hermione had always had long teeth. In "The Goblet of Fire" Harry and Malfoy tried to curse each other, but their spells bounced off of one another. Harry's hit Goyle, which made him sprout green boils. Malfoy's hit Hermione, which made her teeth grow abnormally long. Snape sent Goyle to the hospital wing, but told Hermione that he "saw no difference." What a guy.
4. He exposed Lupin as a werewolf.
Werewolves are highly stigmatized in the wizarding world. It is difficult for them to find acceptance and work. Lupin got a position at Hogwarts and very few people knew his identity. Unfortunately, Snape was one of those people. He revealed Lupin's identity to the school and got him fired. Snape also taught his students how to identify and kill werewolves.
5. Snape was willing to sacrifice Lily's husband and child.
James Potter was ready to sacrifice himself for Lily and Harry. Snape was also ready to sacrifice James and Harry to protect Lily, whom he loved.
6. If Neville was the Chosen One, Snape would still be a Death Eater.
Neville had equal opportunity to Harry to be the Chosen One, but Voldemort chose the latter. The only reason Snape left the Death Eaters was because Voldemort didn't spare Lily when he went after Harry. If Neville had been chosen instead, Snape would still be a Death Eater.
7. He invented a spell that could slice body parts.
In "The Half-Blood Prince" Harry uses the spell "sectumsempra" that Snape invented. It was to be used "for enemies," but other than that Harry had no idea what it did. It literally slices people open so they can bleed to death. Snape invented it when he was a teenager, too.
8. Snape never grew up.
A lot of people use Snape's tragic past to justify his actions. They use James' bullying as a example. James bullying wasn't okay, but he grew and changed from the person he was. He helped his friend facing prejudice. He regretted being a bully and he went on to sacrifice himself to save his wife and son. Snape was resentful and prejudiced from the beginning. He was part of a bigoted group, called his best friend a slur, and went on to bully children.
9. Snape was grossly obsessed with Lily.
Many people think Snape's line "Always" is a romantic line. All it shows is that he was obsessed with a woman and thought he was entitled to her just because she was nice to him. He didn't care about her agency at all.
Snape was not the romantic hero everyone thought he was after they read "The Deathly Hallows". He was an abusive bully that never got past being denied by a woman who deserved better than him.
