DD is 24 and still lives at home.
She has always been hard work, and eventually got diagnosed with ADHD a few years ago, at the age of 19. I split from her father when she was little and he, and his family, along with my family (whom I no longer speak to) have always indulged her and let her do as she wanted, so I always put her difficult behaviour down to that, despite having very firm boundaries at home, and parenting her no differently to how I've parented my younger kids.
Anyway, since the diagnosis (and subsequent medication) her behaviour has got much worse at home, and I find her very, very difficult to deal with.
The main thing is the tantrums! Constant tantrums when something does not go her way. For example yesterday her work made a small error on the rota, and she just had to phone her boss to get the error corrected but she had almost an hour long tantrum before phoning the boss, of screeching, and shouting, and crying very loudly. During the tantrum she said to me that she is the most important person in the world and that everyone needs to realise that. Anything can trigger a tantrum; her boyfriend not doing what she wants, something at work not being as she wants, the doctors surgery making her wait a day for a prescription to be issued. Everything. It's like she's two years old again but obviously being an adult is very hard to deal with. It's also not nice for any of us in the house (me, DH and two younger teenage children).
Secondly, she never stops talking at me; mainly it's ranting about things, but also it's about other things that she might get obsessed about. For example if she has her hair done she will talk about it for hours afterwards saying how much she likes it. She will talk at me at all hours of the day or night, and has even been known to wake me at 2am before to rant at me about something her boyfriend has said. I literally never get any peace.
Thirdly, she treats the place like a hotel and feels like she has priority over everything. She will often go for a bath, lock the door, and be in there for three hours, despite us saying not to take a long time and telling her not to have too many baths as the water bill is huge and we prefer everyone to have showers as much as possible because of this. The other day I had sprayed cleaning fluid on the bath and sink and was about to go back into the bathroom to clean them when she went in and shut the door. She refused to come out when I said I needed to clean in there first and started screaming. She then took hours in there again. She will also cook at any time of day or night, or start ranting in the middle of the night because the internet isn't working quickly and will start screaming.
Any attempts we make to put down boundaries or tell her not to do things just get ignored and it ends up in a tantrum. She had a two hour tantrum last week because DH told her to have a shower rather than a bath as he wanted to use the main bathroom.
I know this all makes me sound horrible, but I am at the end of my tether and feel totally ground down, so please be gentle with replies.