1. When a person is on Facebook so much that their eyes twitch to the bottom right-hand corner, checking to see if they have any notifications purely out of habit, even when they are on a website that is not Facebook.
2. Less common: When a person uses Facebook so much that they respond to non-Facebook-related situations (sometimes in the real world) in ways that would only be used on Facebook.
1. I was on Urban Dictionary the other day, where there are no notifications, but my Facebook twitch made me check the corner every two seconds.
2. Her Facebook twitch was so bad that when she saw me eating a muffin, she proceeded to shout out that she'd like to 'become a fan.'