I became a Ranma fan by accident after reading a forum that recommended it. After that I started to watch the entire anime series, which later lead to me read the manga, since I really wanted conclusion to the Nodoka/Ranma story arc. By this stage I was hooked, which lead me here to become a Ranma fan fiction fan.
Ranma fan-fiction turn offs.
-Fics when Ranma is cured right at the start or when the curse is ignored. I believe it is too major a plot point to ignore or remove.
-Mental challenged Ranma. Okay he's not smart, but not truly dumb either, just ignorant and insensitive on occasion.
-Ignorant of sex Ranma. Seriously, give him some credit no ones that naive and if he was before because of Genma he probably isn't now after going to Furinken school.
-Weapon hating Ranma. This is simple not true, sure he prefers not to use them if he does not have to, but it is clearly shown that Ranma will uses weapons when he faces Saffron and other situations, and I don't remember him procrastinating over it .
-Super sexist, won't hit girls Ranma. Okay he's a bit sexist but that due to the way he was raised. And about the only martial artist Ranma won't hit male or female is Akane, but not girls in general. Point encase is Ranma's first defeat of Shampoo, when Ranma kicks her several feet into the air off the log.
-Fics that are OOC without proper character development. Okay I accept that a character may act differently after 'x' amount of life changing events. However I don't like it when an author simple states that Ranma secretly prefers being female and is really smart, with out telling us why. This is not to say I don't like Ranma-chan fics, because I do as long as the character development is done.
-Over play on the Neko-Ken fear. I don't mind if it has a minor role, but it is annoying if Ranma spends half the story avoiding cats. Plus I prefer it when he masters it.
-Splitting Ranma's curse. This is because I don't like one Ranma getting what he wants while the female Ranma is left in the gutter effectively locked in cursed form. Or shudder worse than that, Ranma X Ranko pairings.
-Most first person and script formatted fics.
However there are some exception but I'm not sure what they are.