Sadly, there are a few people who make what should seem like unnecessary boundary policing feel necessary. I asked for a D/s Sirius/Remus fic one year. Got it, but it also contained bestiality. Not "complete" bestiality, but sure as hell enough that it crossed a line for me. I didn't even think to state that one, and there it was in an exchange fic. ::sigh:: (It was not a small gifts fic, though.)

I've actually just come to the point now where I say "I'm fine with explicit material, but I'm a pretty vanilla sort of girl" in anonymous exchanges. If it's a small exchange or I know the group (like on gaeta_squee), I might be a little more specific, but usually, I'd rather people shoot for under my limits than over them. The other thing I generally add is "canon pairings only" or list the pairings I do like, because there ARE popular pairings that I can't handle in fandoms I like (Simon/River, for example), and it's a nice way to say I'm uncomfortable there.

I really don't have a problem with people listing their dislikes, though. I mean, there are a lot of people that really, really dislike very common tropes. (I like consensual violence in sex, for example. Lots of people don't, and understandably so. I can't stand infidelity. Doesn't bug tons of people.) I think where the problem comes in is the commentary. I don't find "no non-con, violence, or anal, please" offensive in the least, personally, but if someone adds the "because that's ICKY!" part, then it becomes offensive.