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1.
Taking a good hit out of a bowl when there is only resin in it.
"Dude I was totally neffing that bowl."

"Hey man, could I neff that bowl?"

by tippy August 15, 2007
 
2.
Being VERY annoying by posting useless or stupid coments to a forum.
reminding everyone how great your computer is every day.
by CorvetteZ0606 June 07, 2003
 
3.
The act of making plans with someone then not fulfilling the plans you made.
Person 1:Dude are we gonna skate on Friday?
Person 2: Yeah man I'm down anytime!!

-_-_ Friday_-_-
Person 1: Hey man what time are you coming?
Person 2: Dude I can't go
Person 1: ARE YOU SERIOUSLY NEFFING ME RIGHT NOW?? FFFFFFFFFUUUUUUUUUUUUUUU...
by Skate-o-Rama January 19, 2011
 
4.
Neffing is posting on a forum about basically nothing in order to drive up post totals.
An example is replying with only a smiley or one word such as "lol": this causes a lot of useless post. Rules often include - no neffing or you'll have your post count or rank significantly reduced!
by Thresher May 26, 2006