Oh, it happens. To me, it did:

1. I went to HR to complain that my supervisor promoted a fellow call center representative to another department despite the fact I'd been there longer and she had only been working there less than one month. Within the week, HR notified my supervisor, so he put me on a 2-week 'disciplinary plan' (for what, I did nothing wrong!) and then fired me, without giving a legitimate reason since I live in a 'fire at will' state.

2. I went to HR to complain that the man who trained me to engineer the weekend shift at a local radio station had sexually groped me and sexually verbally harassed me. The radio station director called me into his office and fired me, accusing me of making it all up.

3. On a long-term substitute teaching assignment, a student punched me both in the face and the stomach after running amok around the classroom (this student had a reputation for violent outbursts at this school already that the principal was aware of but ignored). When I reported this student to the school principal, he fired me on the spot, citing 'poor classroom management skills.'

There's more but those are the top three I can recall.

So yeah, it happens.