Top 10 Worst Things Severus Snape Did in the Harry Potter Books and Films

We did a list about Dumbledore, and now we'll do one about Snape. This will probably be a bit easier.

The Top Ten

Became a Death Eater
Bullied students

As a teacher, you should not bully your students into learning things while holding them to some really high standards. He does this with most non-Slytherin students.
Murdered Albus Dumbledore

Well, we find out it was planned ahead of time, but it should be quite obvious what we saw. Snape was the one who killed Dumbledore. There's no denying it.
Outed Remus Lupin as a werewolf

This forced Lupin to resign, and Snape mostly did it out of a grudge.
Cared only about Lily Potter, not James Potter or even little Harry Potter

He hated James when he was in school and had no sympathy for little Harry Potter when Voldemort murdered the Potters. He cared more about Lily, and it was all selfishness, really. Sure, it was a sad scene to watch as Snape was hugging the dead Lily, but he only cared about her.
Deducted points from Gryffindor because Hermione Granger was "being an insufferable know-it-all"
Invented curses

It was a spell "for enemies," and its power is quite deadly in the wrong hands (as demonstrated when Harry used it on Draco). In other words, Snape was responsible for creating a deadly spell.
Made Neville Longbottom almost poison his pet toad
Called Lily Potter a Mudblood
Didn't get over Lily Potter hooking up with James Potter

Much of Snape's entire character is based on his somewhat creepy love for Lily when you think about it, along with his lingering resentment toward those who bullied him.

The Newcomers

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Allowed only students with "Outstanding" marks into N.E.W.T.-level Potions classes before the requirement changed to "Exceeds Expectations"
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Tried to cast Sectumsempra on James Potter

The Contenders

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Became a Death Eater