I came into a company to work on a project that my boss had done a lot of work on, previously. The work he had done was trash.

I thought and strategized with co-workers a LOT to try to figure out how to position my proposed changes. I was (I thought) so careful, so respectful, so understanding of how work done under time constraints is going to have some flaws, etc, etc.

All to no avail. The dude was a complete and utter a**hole, I got put on a PIP (performance improvement plan) after I proposed some changes. I ended up just leaving the company.

Leaving worked out well for me, thank goodness. But next time around, I will understand how (some) people react, even when you're specifically brought in to fix things.