How do you block a X friend from sending and being able to sign in on your Facebook?

Go to that person's profile and go to the bottom of the page.There you'll see "Report/Block this Person" and click on it. From there click block this person,and that person won;t be able to see your profile or interact with you in any way. If you have some connections via some Facebook apps the block does not include those apps so you'll have to remove that person from those apps. I hope I helped you with your question.