People who post a long OP about someone, and bend over backwards, and arse over tit, to avoid mentioning whether they're female or male, and go through the entire thread calling said person 'they' and 'them.' It's so exhausting to read, and very irritating. When I put a response, I will put he or she/him or her.. It's got to be one or the other, so based on the OP's posts, I will guess, and pick he or she.
The 'am I pregnant/is their a second blue line' threads, where the OP goes on to post a negative pregnancy test, and 2 out of 3 people say 'yes I see a second line, congratulations baby mama!' 
How old am I? Stupid STUPID threads. When said poster is 48, you get people saying 29, and 70, both of which are ridiculous. She looks her fucking age! Everyone does! Why would you not? 
How much do you earn? Full of 90% bullshit about what posters earn. See also, how much is your house worth, how much savings do you have, how much do you have in your pension? As a pp said, it just turns into a massive bragfest, making other people who have very little feel like shit.
'Oh no, we have a trip to Disneyland in America, leaving this Friday, and I just realised my passport fell out of date in January! '😖 Who the fuck books a multiple 1000 pound holiday and doesn't check the dates of the passports of everyone going, before booking?!
The 'anyone who is size 12 or more, is a chubby fucker' posts, piss me off (and so do those who boak at the thought of being over 8 st 3.)
As several posters have said, suggesting every bit of bad or toxic behaviour, must be ADHD, autism, or dementia. Very often it's NOT, and it's an insult to people with these conditions.
The 'my husband hasn't come home' threads. One a week guaranteed, where the OP posts it at around 11,30pm. (He was due back at 10pm and she is worried SICK.) He returns by 2 or 3am EVERY. SINGLE. TIME.
Threads being deleted with no apparent reason why, and wondering happened.
A poster telling someone else to 'calm down!' Just because they disagree with them. Patronsizing and goady and misogynistic, and made to try and shut the poster down. Whenever anyone has ever done that to me, I just ignore them. Even if someone IS angry, does anyone seriously think saying 'calm down' is going to make them calm down? LOL!
The fact that dripfeeds (from the OP) are now called 'updates.'
Race baiters.
The LTB type posts, that suggest you can just pack up your life into one suitcase, and move to a shiny new life, a new career, a university degree, a young hot new partner, and masses of wealth that you can store in your million pound house.
A poster talking about a useless twatty fat lump of a cocklodger man, who is verbally and physically abusive to her, saying 'but he's a good dad!' NO. No he is NOT!
Man here, Teacher here, GP here, Solicitor here, Magistrate here, etc etc etc.. Just grates on me so bad.
Grief vulturing... eg, 'I was in New York in summer 2000. When I think how close I was to being involved in 9/11, it makes me weep.' 😢 AND when someone has been murdered or gone missing and people start threads with all their private detective shit! GAGGING for new information, and desperate to be the first to break any new news.
OP not returning to their thread.
DNiece, DCat, Ddog, DNephew, DUncle, DAuntie. FFS, just put niece, cat, dog, nephew, uncle, or auntie!
Posters calling others 'unhinged.' Fucking vile thing to say.
Suggestions that gaming is for children, when the majority of gamers are ADULTS! (Shows how little they know! And just proves they are ignorant.)
The patronising 'I couldn't get worked up about that' phrase. Someone mentions something that another poster deems silly, and tries to make the poster feel daft by belittling them.
When someone says their mum is a nightmare, and someone dives in and says 'be grateful you HAVE a mum! I lost my lovely mum 10 years ago!' I am sorry for anyone who has lost their mum, but doing this is just is out of order IMO.
TV snobs/book snobs/food snobs who look down on anyone who watches Love Island, or Big Brother, or who don't cook from scratch often, or who read take a break and that's life magazines!
People who look down their nose at social housing tenants, and seem to berate and spit bile at them for getting a 'free house,' and being a 'benefits scrounger.' Whilst insisting they should give it up as soon as they hit £30K household income, so someone 'more deserving' can get it. Not able to comprehend the fact that if the person in the social housing home who is possibly reasonably comfortable and has surplus income, would be in the other person's position if they swapped their £420 a month social housing for a £1100 a month private let. By the way, my local housing association have 7000 properties and 60% of the tenants have a job! (And most of the 40% are pensioners/retired, or unable to work because of health conditions.)