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1.
"Not For British School Kids"

Uses:
1. In place of a swear word
2. Describing a topic that is obscene, disgusting, or in general "not for kids"

Origin: Circa 1998
At the snopes.com message board, an obviously irate woman posted saying the other posters should watch their language, because there were British school children reading the message board. From then on, as a joke, the other snopesters started using NFBSK in place of swear words or in the subject lines of topics that might not be suitable for children (or the squeamish).
1. I moved one Jenga block and the whole NFBSKing thing fell down!
2. I'll tell you about my surgery, but I must warn you, it might get a little NFBSK.
by birdman August 04, 2004
 
2.
Acronym: Not For British School Kids

Created on the snopes.com message board. Can be used in place of a curse word, or to describe something as inappropriate.
I don't need your NFBSKing attitude!
Man, this topic is a bit NFBSK.
by NuclearMosquito July 29, 2004
 
3.
Not For British School Kids
Meaning obscene or adult in nature.
Also used to censor somthing.
"She kicked the NFBSK out of that guy."
"Um, I don't think johnny should see that movie, its kinds NFBSK if you know what I mean."
by ditto September 13, 2003
 
4.
Originated on the snopes.com message board.
NFBSK! That post in the NFBSK forum in really NFBSKed up!
by DarkDan October 10, 2003