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.

A buzz word being used to refer to creators and influencers forming or encouraging unhealthy relationships with their fans. Usually used in the context of young audiences feeling they have a relationship with the influencer due to the huge amount of the influencer’s content they consume. The influencer in question, however, is unaware of the fan’s existence other than the general knowledge of having fans. Common examples include Dream and his stans. These relationships are exacerbated by the influencers confirming they have more than a creator-to-viewer relationship.

The word is circulating due to various YouTube essays about the phenomenon using the word, and therefore people who enjoy complaining about influencers repeating what they heard in the video in any comments section they can find.