In my first flat which was an old house split into two, I was on my day off minding my own business and my boyfriend who I lived with was at work.
I heard a key in the lock and got up because he wasn't due home yet and my LL and her husband had let themselves in! They gave us all notice and put the flats on the market a couple of months later so I think they had come at a time when they thought no one was home to give the place a look over before they gave us all notice and sold up.
In our next property, my boyfriend and I were there for a couple of years but ultimately broke up. He stayed in the flat for another 6 months but when he moved out he couldn't get the day off to do the handover with the LL.
My parents had given us the deposit which we should have gotten back since everything was in as good condition as when we'd moved in, so I offered to do the final check for him and took our mutual friend as company.
The LL started saying we'd damaged this, that and the other, it needed painting, a professional clean etc so my friend started quietly taking pictures on his phone - well! The LL got very angry and in his face, he was clearly not happy that the friend would have proof he was talking nonsense! We were as polite as anything but said if he wanted to keep the deposit we would be fighting to get it back and we were entitled to our own evidence to prove we hadn't broken the kitchen units etc.
We did get the deposit back funnily enough, but LL wasn't happy about it.
First place exH and I rented the LL was notoriously nosey, would spy on the tenants and had been caught in peoples flats before if they left the door unlocked. This was in a rural village, LL owned a converted house and lived across the road.
I remember one day she came knocking on my door to ask me why someone my husband and I knew was going inside with the guy in the other flat. She refused to believe me that they actually knew each other and were friends too for some bizarre reason!
It's a little village woman, mostly everyone around the same age as us knew each other in some way or another and it wasn't some nefarious plot going on, it was probably a cup of tea!
Couldn't believe she'd actually come to ask me what they were doing together, like I would know anyway 
Current LL is lovely but recently upstairs had a plumbing issue so they asked if I would mind if the plumber came into mine to check it hadn't affected my pipes. I said yes that was fine.
Plumber turns up with a guy who I figure is his assistant maybe? Neither are wearing masks so I asked if they had any, plumber did and put his on, assistant doesn't but has a scarf.
Plumber starts work, assistant just stands chatting. Both their mask and scarf keep falling down 
Then the LL turs up (wearing a well fitting mask) and comes to check with plumber how things are so there are now 3 of them all in my not very large kitchen while I'm watching them from the living room.
LL and assistant guy leave together and I poke my head into kitchen to ask how it's going. Plumber mentions that assistant guy is actually LL's cousin and nothing to do with him, had clearly just come for a nosey round during a visit or something 
Lockdown fun 
Most flats/houses I've rented as an adult have had an issue with rising damp or mould of some sort, this place is thankfully free of both! 