Had an HMO of Polish guys next door for several years - like a poster mentioned above, an absolute delight. Polite, clean, friendly and civic-minded.
The landlord sold up to the council, and the place was refitted. A single mum was moved in because she had kids in double figures and the layout suited a large family. They actually started ok, the house was immaculate, and the kids were lovely.
But when the mother got a boyfriend and moved him in, it went downhill shockingly rapidly - he was involved in nasty things with scary people and the DV started as soon as he got his foot in the door.
It is staggering how one single person can change a whole neighbourhood. He managed to bring the whole place down into the gutter in mere months. He was eventually very violently assaulted for not paying money owed to one of the aforementioned scary people.(We know this because of the screaming while the assault was happening, that he would pay, he just needed time.) The single mum took the opportunity handed to her and vanished while he was hospitalised in a coma. We moved not long after.
A few houses later.......We had a neighbour who decided that simply because we didn't have a car and she did that our drive should be hers, and she parked there despite our objections (she had a small baby, dont you know) - She was convinced that we should just suck it up, and when we added a barrier to our drive, started a feud that should only really be reserved for warring royalty over the crown - not a scappy drive in a sad little town in the Midlands. She tried to poison our cats to' show us'
Then we had a little old lady who used to use our emergency key to let herself in after we left for work, fuss our cats and steal our little old dog for company and sneak him back home before we got in. We didn't know until she was dobbed in by her daughter because we had mentioned we were worried and paying for vet tests as the dog was so shattered in the evenings. Our diva of a cat Queenie, ended up adopting her, and they both lived together, doting on each other outrageously for several years. (No word of a lie, she bought the Queenie her own throne)