I am pretty chill about following people, but I will unfollow people who post mostly about their religion. I will also unfollow atheists who post mostly about atheism.
I am an atheist myself, but I am very "live and let live" about religion/atheism and so I guess I don't really want to dwell on it on Twitter. Oh and also, if people post explicit stuff about their sex lives, then I'm generally out too.
What causes you to unfollow someone on Twitter?