give 'em whiplash
What's one or two things that make you "nope" out of an rp, no matter how promising?
When it's obvious that no matter what you do, the other person's character fulfills the RPer's plans for that particular RP. They don't allow the character to develop naturally and react to the stimulus put forth. They push through any obstacle to accomplish the "Goals" of the RP.
I've seen this quite a bit; characters that barely acknowledge the events occurring around them, as if they exist in a little bubble within the RP. The way I see it, it's usually an egotistical thing. Many characters ignore, dismiss, or scoff at anything that would usually have an impact on a real person. It's almost like a display of power for them to wave their hands at everything laid out before them.
Personally, my biggest deal breaker is any setting that gives absolute freedom to the players. I mean, giving people freedom to play whomever they want sounds great and all, but it's usually infeasible. If you let someone play as the lonely king of the corner of the world, chances are they will sit in the corner of the world and mope about how people don't come to the corner of the world. I don't think I've ever seen really spread out games like that ever last longer than a page.
when shadow the edgehog (totally OC guise, and not ripped off from an anime character) appears in the character sign ups and you're like 'psh no way he's gonna be accepted' but then the gm goes 'haha thats a great character, he can exist' and you're just like 'fuck'
This annoys me so damn much. Why do you even have an application there when you're just going to accept any tripe that gets posted at all? Double disgust points if it says something about their "mysterious past" or amnesia. Whatever, you're just lazy and don't want to bother with a backstory.