fbil 

Future brother in law. This designation can also extend to the siblings of the engaged couple. (See example)

Joel: when my brother proposes to your sister, we will be FBILs!

Aaron: best day ever!

fbil by anjfbil February 7, 2013

FBIL 

Future Brother In Law

My FBIL is coming down this weekend
future brother in law FBIL

FBIL by TheRealCuddFoo February 23, 2011

fbil 

an acronym for future brother in law

my fbil better watch himself before my bridezilla sister gets all crazy on his ass.

fbil by TheRealCuddFoo February 23, 2011