Hmm.. I hate the people who always brag about their role-playing abilities, ie; Great grammar, spelling, depth, ext*
And when they finally post its something along the lines of;
"they walks over to that Guy and nods."
Nothing else. A simple sentence or something, and gives you almost nothing to work with.
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Another thing is when your really into a roleplay, and your getting out good length- detailed posts often and everything, and they just give you the most worthless replies that take forever and just make you want to cringe. I've had a MILLION times where I have a good idea for a plot or something, and someone just ruins it and kills the fun or I have to carry the whole roleplay.