I've mentioned this on another thread.
The school didn't tell me until after I'd signed my contract that my predecessor was staying on at the school.
He'd had an affair with an NQT and his wife had found out. (Apparently, some pupils had phoned his wife and asked for the girlfriend by name...) Cue the "nervous breakdown" and "depression". An agreement had been made that he could take a step down on a conserved salary.
I reckon that he and his pals had expected the school to say "Nooooooo. Stay in post!"
Anyway, there was clearly resentment towards me and all sorts of dirty tricks. e.g. On my first day, I was told that the keys to my room had disappeared..I'd be called out to another class to deal with discipline and would return to my room just as my predecessor was disappearing down the corridor...and would find my door locked.
I told my HT and - God bless him - he believed me. (I was worried that he'd think that I was loopy.) He had every lock in the dept changed and I was given a master key.
Nevertheless, the predecessor and his cronies persisted in trying to put me in my place.
One day, I was sitting in the staffroom when a maths teacher asked for help with a crossword puzzle. The room was full. One member of the SLT was sitting opposite me, reading The Scotsman.
My predecessor wasn't there: he had signed himself off with stress yet again.
I said "Oh sorry - I've always been rubbish at cryptic crosswords."
Predecessor's crony: "[Predecessor] would have known the answer."
I heard my voice saying "I might be shite, but at least I'm at my work."
Silence. Opposite me, I saw the Assistant Headteacher's Scotsman shaking.
To this day, I maintain that I didn't mean to say what I did - it was as if an outside force had taken me over. It stopped the harassment, however.