Made famous by Special Agent Leroy Jethro Gibbs (Mark Harmon) on the t.v. show NCIS, this is an open-handed slap to the back of the head. This is usually done in response to an act of stupidity. Done in a half-serious way to show power.
Once at work, I was playing Tetris on my computer. When the boss saw, he Gibbs slapped the hell outta me!
When one joins facebook, they feel compelled to add any person that they might know, resulting in cases with 20 or 30+ friends showing up in their "recent activity". This is common throughout the first few weeks of joining and usually slows down when around 200 friends accept.
"Dude, you got over 100 friends in a day, what the hell happened?" "I guess I was on a bit of a friend binge."