I'll never forget the day that one coworker decided she hated me. She was talking to a coworker about a problem related to code that I was one of two primary authors of. I turned around and interjected, what she was trying to do was already solved if she understood a little more about how the data was stored.

Her face just went blank.

"That's great. Simple. Concise. You must think you're so smart."

She then ranted for a couple minutes about how hard her job is and that I have no idea what I'm talking about etc. etc. until I interjected again "It would be a lot easier to help you if you weren't being so aggressive."

Well she flipped her shit at that one. I ended up going directly to the HR office, shaking, walked past everyone and straight to the main guy's office who I'd never talked to before and just blurted out "I need help with an aggressive coworker." He closed the door and we talked. I went home.

It took a few days for them to find me at fault. The woman who bitched me out goes to lunch with the CEO and his friends every day. She'd worked there for basically her whole career. There was no way they were going to even slap her on the wrist. But they saw me as a troublemaker for it.

I saw many more incidents of her doing this to people, bringing someone to tears in front of everyone once. The biggest lesson I got out of this was that HR is not your friend.