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1.
mbn
1. stands for "must be nice" and used sarcastically when someone tells you something that makes them sounds wealthy, carefree, or conceited.
Wealthy Chick: My parents, my sister and I are going to Aruba for Christmas for a week then to Argentina and Brazil to spend the New Year.

Poorer Friend: MBN! shit!!!

Wealthy Chick: What does 'mbn" mean?

Poorer Friend: it means that it Must Be Nice, mutherfucka! Tell your parents to hook ME up!
by El Muñeco December 08, 2005
 
2.
mbn
must be nice..........
GuyA: Damn I'm full, huge steak dinner.
GuyB: I'm eating chicken Ramen, mbn.
by wikked January 06, 2005
 
3.
Acronym for MUST BE NICE. Usually used on Facebook when someone posts pictures of a fancy car or house.
Brian: Check out my $68,000 Honda

Joey:M.B.N
by BAUWLUH August 17, 2011
 
4.
MBN
Jackronyn for MasturBation Nation - A group of outstanding (self proclaimed) men, linked by messaging technology to share in inappropriate comments, sarcasm, and random shenanigans.
Girl A: "Look at that group of extremely hot guys texting inappropriate, sarcastic, highly intellectual messages."

Girl B: "Hot is right. I have always dreamt of being the centerpiece in an MBN circle twerk."
by justsanotherdude December 02, 2013