Turn offs (these seem to be more easy to come up with, for whatever reason...)
-"Extreme post processing," including, but not limited to, the HDR hole
-Anything for anything's sake
-Filter whoring (as Lon delicately put it)
-Lomography/Bokeh/Hipsters thinking it's ironic to use a Nikon F because 'omg it's so 19th century'/it's all the same
...

One of my former professors, when assigning projects about social issues, had a list of images and subjects that were not acceptable... which stimied most of the students. The list had everything from "kittens" to the most controversial subjects of the time on it: "abortion, war in Iraq, eating disorders..." and so on. In time, I decided I'd never make images about those subjects, because they were done to death.