FNFN, more commonly known as 'Friday Night Fight Night'.

This spectacle generally occurs each Friday, following a hard working week by the male, the main breadwinner, of the relationship.
After completing the working week his 'significant' other decides to 'get up in his grill' about insignificant futile problems, that only women feel the need to discuss.
This ultimately leaves the male losing precious beer time on his Friday evening, causing a serious lack of patience.
The alcohol fuelled, peer pressured arguments that prevail towards the psycho that bought them on herself have been commonly referred to as Friday Night Fight Night.

The abbreviation came about following common use throughout feeds and text messaging, to save the male losing anymore beer time on a Friday evening.

Note this was not written on a Friday Evening.
Guy 1: Damn psycho didn't bring me breakfast in bed this morning...
Guy 2: Screw that, FNFN I assume then?
Guy 3: Yeah for sure

or....

Guy 1: Mate, hold my beer, Psycho calling me
Other Guys: hahaha, FNFN

or....

Psycho: I kinda wanted to do something with just you tonight.
Guy: Really? you REALLY want a FNFN?
by breadwinner100 February 19, 2010
Get the FNFN mug.