I've had people walk in.
The first one I was upstairs, heard the door go, went tot he top of the stairs bloke asks for 'Fred' I say no he doesn't live hear, he said yes he does, ho told me he did, he'd told him the street and the white door, pointed out door was gray. He kept arguing, I got quite angry and told him to leave now - his gf/wife had followed him in and had to tell him I probably did know who lived in my house.
Different place, I lived next door and opposite a hostel for recovering alcoholics, one got the number wrong and walked in to my kitchen, was actually really nice, went to the hostel then came back to appologise again.
When I leave the window open there is a cat who lets himself in and settles down on the settee. He has a collar so must have a home.
I once put petrol in my car, after I had paid I went back to my car opened the door and thought, "my car doesn't have leather seats" fortunately the guy who's car it was thought it was funny.
I was also once in a hotel, had taken a bath, opened the bathroom door in only a towel to find a member of staff and another resident, they had assigned him my room. It was a training course so met him again at dinner.
The best on is my friend's incident, he lives on the 7th floor. He was woken up by someone letting themselves in via the balcony. He'd been in the flat above and couldn't get out the door so jumped and caught on to friend's anti pigeon netting.