As you can see, my list of things that are a hard "no" isn't too extensive, and if there's something the site hasn't listed that you'd like to try out, go ahead and pitch it to me. If it's not on the list of limits, there's a good chance I'll indulge you!
To make some of my preferences a bit clearer, I'll add a couple things here as well.
Fantasy/Interspecies: See title.
Seriously, though. Most of my RPs will be part of the Fantasy or Supernatural genres, which means monster girls, my dudes. Probably the easiest way to my heart.
Clothing Play/Clothed Sex: You have no idea how much this gets me going. If a girl gets dressed up skimpy or in a costume or anything, it drives me nuts.
I'm also a big fan of said special clothes or average clothes being ripped or tugged away just enough, or penetration through stretchy clothes, or body paint/writing, or... Well, you get the point.
Recreational Usage of Powers: If a character has superpowers, extra appendages, or can use magic, and they don't abuse the hell out of they powers for everything they're worth during sex, that character is blind and must be shown the way.
Worldbuilding: As much as my RPs here are likely to act as wish fulfillment, I haven't lost an interest in telling a good story. I like everything in the plot to happen for a reason, and for the narrative to be taken as seriously as any other.
Plus, I guarantee, if the characters are fleshed out and have good chemistry, the setting is interesting and unique, and the plot progresses in a way that makes total sense, the ecchi stuff will be a lot more satisfying.
Love Triangles/Harems: Call me greedy.
Mainly, I really like this dynamic because it allows for interactions that you wouldn't get otherwise, as well as the potential for a wide array of interesting and unique characters in a plotline. Of course, I'll also write characters in Reverse Harems for this same reason.