Please find enclosed in this post a definitive list of all the banned words you can't use when naming your character in Dark Souls II. Also, a warning: there are some seriously hilarious/disgusting/terrifying words in this list.
What surprises me most about the list is the commitment. There are a lot of alternate spellings of the same word that are completely banned.
erekshun masterb8 sekks
And also some words I totally wouldn't have expected to see on a list like this:
dilligaf dingleberry epeen hairy bush lemonparty mandingo
Simply put, this is a pretty incredible and definitive list. Good job From Software.
You can find the whole list here.