Stands for: No Fucks Given. This is a type of mood or feeling, such as being care-free, easy-going, not caring what people think of you or your actions. Also meaning " no fucks where given today" kind of tone but shorter and quicker to say. Similar to saying YOLO, but better and non-mainstream.
Me: I'm gonna wear socks with sandles. NFG!
ME: No fucks given kid.