Whoa, seems like I write a lot of the things that people seem to loathe. N/C, slave, etc. To each his own, though.
My limits would be incest, minor(pedo), beast, mpreg, scat, vore, futanari, inflation, fur... First three just because they irk me (don't care if others write it though, not going to go after anyone with a pitchfork), and the rest just because they aren't my thing, and even if they were, not sure I could pull them off in writing at all...