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1.
The inability to post anything potentially objectionable or politically incorrect to your facebook account out of fear that your boss or co-worker may see it and exact retribution or blackmail.
"Man, I would like to post this article about why marijuana should be decriminalized, but I can't because my boss could see it and then, there goes my promotion". "Dude, you're facebook cockblocked, for real".
by mp2009 February 04, 2009
 
2.
Most often when a male encounters a female and gets the facebook add. The newly met female posts something flirty and is quickly met with a post right above by a girlfriend or the girlfriend's friend.

This is intended to let the male know that she read this new girl's post and does not approve of it.

NOTE: To prevent facebook cockblocks send private messages in the future.
Matt's facebook wall:

GF's post: Heyy babe, just wanted to say i love you so much! (translation: dont you fucking respond to that post below or i will rip off your nuts)

Shirley's post: hey matt, i had a great time last night with you! give me a call sometime :)

(later)
Matt: Yeah i met this hot chick last night at the concert, but lauren facebook cockblocked me when she wrote on my wall
by gordonchem September 29, 2009