Facebook Shark 

a Facebook user who logs on and lies in wait for someone else to log on, so that they can immediately trap them in a conversation.

Hm, I think I'll log into Facebook.
2 seconds later:
new message from Jason: HEY!!!!!
Damn, what a Facebook Shark.

Facebook Shark by PoisonPen May 23, 2009

Facebook Shark 

When you are so desperate for attention and a laff from your 5,000 facebook friends you devote 50% of your page trashing someone. All your 5,000 insecure facebook friends think you're a leader, a killer shark, so they following along with all the fun and laffs to gain your approval and friendship!

Shhhhhh...that bitch doesn't even think we are talking about her. No one gives a shit about her, but I'm going to spend my time devoting 50% of my FB page to her and all of you will spend your time reading about her. Man, I hope I get some laffs out of this, because being a Facebook Shark makes me feel important and hopefully feared by others I think are trying to cross me.

Facebook Shark by Laff is spelled laugh November 9, 2009

Facebook Shark 

A fiercely opionated friend with a voracious appetite for debate. Someone who will pounce on loose comments and opinions and attack without mercy.

Related to:

Facebook Chumming:
The practice of luring friends (Facebook Sharks), by throwing "chum" into the water. Chum usually consists of political or religious comments... far too tempting for a Shark to ignore. The water in this case would be status updates and walls.

When someone knows a Facebook shark is around... making a comment like,

"The Church isn't interested in money or power...."

Facebook Shark by NeilPeel December 23, 2010