What does NBF stand for?

NBF / (Not Being Funny). Used in situations where a person is trying to explain a concept and make it explicitly clear that they are not being funny or humorous about it.

Speaker 1: If i don’t get a car for my birthday, nbf, my mom is going to hear about it to no end.

NBF / (New Best Friend). When a person has become close friends with another person, this expression can be used to demonstrate that they are their new best friend.

Speaker 1: omg you like Backstreet boys too!? I love them! You are my NBF!!

NBF / (Natural Bitch Face). This phrase can be applied to people that naturally look like they are in a bad mood all the time. Somebody who always looks pissed off by default.

Speaker 1: Did you see Sarah today? He looks like he is super upset about something?
Speaker 2: I wouldn’t worry about it, she has a nbf so it’s probably no big deal.