Block Twitter/Facebook in your /etc/hosts

gistfile1.txt

# Block Facebook IPv4
127.0.0.1   www.facebook.com
127.0.0.1   facebook.com
127.0.0.1   login.facebook.com
127.0.0.1   www.login.facebook.com
127.0.0.1   fbcdn.net
127.0.0.1   www.fbcdn.net
127.0.0.1   fbcdn.com
127.0.0.1   www.fbcdn.com
127.0.0.1   static.ak.fbcdn.net
127.0.0.1   static.ak.connect.facebook.com
127.0.0.1   connect.facebook.net
127.0.0.1   www.connect.facebook.net
0.0.0.0     meta.com
0.0.0.0     www.meta.com


# Block Twitter
127.0.0.1 www.twitter.com
127.0.0.1 twitter.com
127.0.0.1   apps.facebook.com

# Block Facebook IPv6
fe80::1%lo0 facebook.com
fe80::1%lo0 login.facebook.com
fe80::1%lo0 www.login.facebook.com
fe80::1%lo0 fbcdn.net
fe80::1%lo0 www.fbcdn.net
fe80::1%lo0 fbcdn.com
fe80::1%lo0 www.fbcdn.com
fe80::1%lo0 static.ak.fbcdn.net
fe80::1%lo0 static.ak.connect.facebook.com
fe80::1%lo0 connect.facebook.net
fe80::1%lo0 www.connect.facebook.net
fe80::1%lo0 apps.facebook.com

In addition to that, I also added 0.0.0.0 api.twitter.com

If you are using Pi-Hole for blocking just Facebook, you can plug these into the admin web console as wildcard domains:

facebook.com
facebook.net
fbcdn.com
fbcdn.net
fbsbx.com
fbsbx.net
fburl.com
fb.me
fb.com
m.me
messenger.com

Pi-hole wildcard domains match on regex like: (\.|^)facebook\.com$