look up any word, like fleek:
 
1.
when you go to check your facebook, get sucked in and realize an hour has passed and realize you just wasted so much time.
Rob: "I had the worst facebook blackout last night, I was supposed to be doing homework and I checked my facebook and I wasted an hour"
Kelly: "Sucks."
by beach_bum7145 November 13, 2008
 
2.
A.) When, upon waking, one realizes that you went on Facebook last night blacked out - resulting in untold horrors.

B.) The actions of going on Facebook while in the middle of a alcohol-induced blackout.
A.) "Why did I send six vile Facebook messages last night to people I barely know? Oh, it must have been a Facebook Blackout..."

B) "Duuudeee...I am so going to send messages to this bitch!"

"Dude, don't do it, your in the middle of a Facebook blackout!"
by Wallace Carlos June 02, 2009
 
3.
The lack of realization that one has made an entry, usually embarassing,on a Facebook profile. Usually discovered the following day.
Allan: "I can't believe you took the Which Ghetto Booty Do You Have Quiz."

Wes: "I did? I can't remember. I totally had Facebook Blackout. I bet it was Badunkadunk."
by bajongy September 04, 2009