Two big ones for me which unfortunately were traits of my ex gf, otherwise we would have been great...
1. Taking everything as a personal slight and getting offended. It makes conversation difficult because you have to censor everything you say in your head before you say it because you're thinking "will she take this the wrong way, will she use this as an excuse to get offended". I think its a power thing because people want to do that then make you apologise and suck up to them, but I didn't go along with that, I just left her to stew in it, but it would kill the mood so many times when we were out doing stuff together and I'd make an innocuous comment that she would choose to take as a personal criticism and then we'd just both sit in silence.
2. Making big issues out of things that don't matter. Life is stressful enough without turning small things in to big deals. One of her things was getting annoyed if I wanted to stop at the cashpoint on the way to somewhere if we were going out. She would say well lets just go somewhere where we can pay by card then. I can understand if we had to queue for ages but even if there was no queue, when it would take less than a minute to get cash out, she would get annoyed that I was "wasting time" by going to the cash point. Another one was if you were outdoors and came inside with sunglasses on, if you didn't take them off literally the moment you walked through the door she was fussing about wearing sunglasses indoors. So if you were carrying stuff and came in a building, walking upstairs and wanted to get upstairs before putting your bag down to take your sunglasses off, you'd already have her chirping while you were walking upstairs about 'why are you wearing sunglasses indoors it just looks weird". Another classic was if you went out to order drinks or food somewhere, you could bet any money that there would be issues about what you chose, say you decided to order the same thing that you ordered last time, there were complaints "why are you getting that again?" "why don't you try to do something different". One time because I ordered a mango frappuccino at Starbucks twice on consecutive times we had been there, it started her chirping and fussing about it and led to some major thing with her saying I wasn't open minded enough....ffs it was just a bloody frappucino not a major life decision. And this 'wanting variety' thing would cause nightmares when doing stuff with her, she'd say she wanted to do stuff, so I'd suggest lets go to X, "no, don't feel like that', lets go to Y, "no, we always go there", ok then lets do Z, "no I'm not interested". It was like trying to entertain a child and constantly having to stay one step ahead to think of something new.
For a while I dealt with all this kind of stuff by just accepting that she would moan about things but it just made being with her stressful. If we met up after a hard tiring day at work I couldn't really relax with her, I'd be constantly trying to evaluate every small decision I was going to take, to try and avoid her having stuff to fuss about.
In the end I just lost interest in the relationship.