I objectively look at what people are likely to write when it doesn't come from my 'likes' list, and typically decide that things such as scat, non-con, and bestiality don't fall under that.

Exception is my one major squick. And there's a couple of unlikely-to-be-written kinks that I also include because some of my likes are typically combined with them (major one is dub-con: some parts of that I really like, others are squicks for me).