Well, the one that got me thrown out of my last church was identifying as a woman (and, more specifically, transitioning to live as a woman). My erstwhile vicar (with the agreement of the church council) believed that I couldn't be a Christian and do this, because I was "denying God's creation".

I might have expected it of more fundamentalist (particularly US) churches, but this, scarily, was a completely mainstream Church of England church.