I haven't had time to set up a test user and actually walk through what happens.
However, the documentation I have found says that "Ignore" controls what you see. Not what they see. So, if you ignore someone, you won't see their posts. They can still see your posts. You will, unfortunatley, be able to see when they like your content. And, in a page that's got stuff you have ignroed, there's a link to show it to you. So, some self-discipline to not go looking for trouble is required.
I suspect some folks would like to have a full "block" feature, which would also keep the blocked person from seeing your stuff. My reading so far is that XenForo does not supply this natively. It would likely require Morrus to install a plug-in, which may not come quickly.