How to block someone on Facebook without them knowing?

[kala]

Yes, I've had to do this to a boy.

1. Hover your cursor over their name.
2. Go to the Friend button on their profile pop-up
3. Scroll down to Settings
4. It says All Updates, Most Updates, or Only Important Updates - - Select Only Important Updates.
5. Uncheck everything else below it like life events, etc.

You will never see this person again and they will remain your friend.

P.S. My answer will stop all of HER posts from showing up on your FB page. She will still see your posts, but you won't have to look at hers anymore.