The act of removing an actual sibling from your Facebook's sibling list. This is usually done after the sibling does something embarrassing to your profile, making you want to forget that you're related.
Man 1: "Dude, your mother just posted 'I love you' all over your wall!"
Man 2: "I know. It's so annoying. I'm going to desibling her when I get back home."
Man 1: "No, you should keep it! It's so cute!"