Anyone who's ever written with someone else has certain pet peeves. Some things that don't gel with the way you write. A large part of it is getting to know and understand the styles of new partners. Over time you understand what works with whom and what doesn't. But somethings just don't work out, no matter how much you try to give people some leeway, some shit will always make you cringe. This isn't a personal attack against anyone specific, just a general curiosity to see what shit bothers most people.

Alright that said, my two least favourite traits are God Mode-ing and Unwillingness to Improv/Diverge from a Script.

What are yours?

mixing up tenses and or writing in opposing tenses. I. E. someone is writing in 3rd person and the responder writes in first. It's just really hard to stay engaged. 

People that write for you. 

"I whistle at you and you love it" or We run through gunfire, while I take shots back, you get shot in the ass.

Just do what you want and I'll react to it, thank you. 

Well damn, people just took the ones I had.

Uhm, mixing tenses for sure, mixing 1st and 3rd person.

It is also weird when people RP in 2nd person, I saw it once, very confusing.

I also hate when you make a really good -point- or really do a nice scene or paragraph, whatever and other person decides to shit on it. Like, you are playing poker and you write how you got lucky, drew another ace, bla bla, waitress had big boobs or something.

And they take your part and do "one up" ah, your four aces have no match for my royal flush, 8 times in a row.

I agree 100% on the people that write for you. It's really annoying and makes you not want to write with said person anymore.

Yup nothing worse than being a spectator to your own story, being made to do stuff you know your character would never do.

As for tenses and perspectives, I'm usually fine with either as long as its consistent. Once you start changing shit up randomly, then like Honey said, it's hard to stay engaged.

Heck I'd say the same for formatting too. Just pick a style, colour, italic/bold whatever and stick with it. 

People already mentioned them, but "godmodding" like the one upping mentioned above.  Drastically taking the story in a direction that directly opposes what had been set up previously. Switching tenses, and long paragraphs of dialogue coming from my character with no actual discussion with me OOC. 

I'm quite relaxed about it to be honest although I can understand where Mercy_Fiorentino (and many other females) get annoyed.

I write with people who seem to be on the same page as me, don''t take it too seriously and like to have fun.

If i don't like something, I don't engage.