Blocking someone
Blocking is the tool for when you simply don't want anything more to do with someone. Use the Block button on their card or profile.
When you block someone, any existing friendship between you ends, and direct interaction (messaging, likes, replies, reposts) is restricted. Blocks do not affect visibility as the site is entirely public and simply logging out would circumvent that. It's a personal setting - it changes your own experience rather than penalising the other person.
You can reverse it at any time: a blocked person's card shows an Unblock button.
Blocking is about your comfort. If someone is being abusive - not just annoying - please also report the abusive content so it can be dealt with.