In my career, I've had to deal with two crazy coworkers. The first one worked directly with me. I knew she had a vicious streak, but she was wildly inconsistent - kind and thoughtful one moment, fucking nasty another. And she had no inhibitions about running down coworkers and even superiors, which I thought was stupid. But I never dreamed she'd swivel her guns towards me.
Until the day I took a call at my desk. It had a single ring, meaning it was an internal call. But when I answered it, the person on the phone said, "You don't know who I am and I'm not going to tell you. But there's something you need to know about your coworker. She's filed an official report with administration claiming you're taking kickbacks from the companies you're doing business with in exchange for throwing business their way."
I boggled. And said, "Who is this?"
"Nobody you know. But because of the report, an investigation was begun, until a Powerful Person made it clear she did not believe it, and quashed the investigation. And then ordered me to tell you what happened, because YOU NEED TO KNOW what your coworker is capable of doing."
(Because of the nature of my work at that time, not only would taking kickbacks lead to termination, it probably also would've led to criminal charges. So this was a big deal.)
I got off the phone, and I still couldn't believe it. So I kept quiet, and waited until my coworker left for one of her leisurely lunch breaks. She always kept her pc unlocked and her work email account logged in. So while she was gone, I went through her Sent box, and found the email where she made the false accusation about me. I made a printout of the email and took it home and filed it away.
She tried setting me up again several months later, by sticking a purchase agreement for a negotiated price with a past-due deadline at the bottom of my incoming box. When I worked my way through my inbox and found it, I was horrified. How could I have failed to get this done on time? Missing the deadline added thousands to our cost. So I gritted my teeth and turned myself in to our supervisor. Instead of writing me up, she asked lots of detailed questions, then shrugged and told me to forget about it. "But aren't you going to write me up?"
"Will you stop and THINK about it? About how something that OLD ended up buried underneath all the NEW work in your inbox? Where do you think that order really came from?" I got the clue and walked out.
TL;DR: never assume your bosses aren't aware of what's REALLY going on behind your (and their) backs.