The colloquial British- and Irish-English noun Black-Eye Friday, also Black-Eyed Friday, designates the last Friday before Christmas.

This noun refers to the high number of fights caused by revellers on that day.

The following explanations are from To the bartenders serving me this Christmas, a few tips for you…, by the arts journalist Alice Jones, published in The Independent (London, England) of Saturday 20^th December 2014 [page 37, column 2]:

“Black Eye Friday” is probably the worst of a bad bunch. It refers to the most drunken night of the year, the Friday before Christmas when a pile-up of work events, parties, hangovers and the prospect of a week or two off combine in a big, boozy mess. For some, inevitably, it ends in fighting and a trip to A&E. Alcohol consumption on Black Eye Friday jumps 114 per cent compared with an average Friday. According to figures released by Public Health England, £3.7bn was spent on alcohol in December last year, 25 per cent more than in November.
The knock-on effects? It’s hard to know where to start: cash squandered, productivity dented, liver damaged, reputations tattered, not to mention the strain on emergency services, called on to mop up the fisticuffs and vomit. Last December in London there were almost 6,200 alcohol-related ambulance call-outs, or more than 200 a day.

The earliest occurrences of the noun Black-Eye Friday, also Black-Eyed Friday, that I have found are as follows, in chronological order:

1-: From the column In Brief, published in the Irish Independent (Dublin, County Dublin, Ireland) of Friday 23^rd December 2005 [page 9, column 1]:

Police set for Black Eye Friday
POLICE in the North will put in place extra resources today—the day referred to by many officers as ‘Black Eyed Friday’—to deal with the expected annual upsurge in public house assaults.
Commander for the Moyle council area in Co Antrim, Chief Inspector Paul Bailie, said officers in his area will be ready for any trouble.

2-: From The annual holly heist, about traditional Christmases in Cumbria, by the British novelist and short-story writer Sarah Hall (born 1974), published in The Independent (London, England) of Sunday 23^rd December 2007 [page 18, column 3]:

Yuletide in the loft of England can be lovely, what with all the bright twilighting and white-capped mountains, the adorable old-fashioned garlanding of villages and our undeniable Northern cheer. It can also be a depraved and ruinous affair, a time of power-cuts, amateur goose slaughter in the outhouse and Black-eye Friday in the market towns—that violent, incontinent form of delinquency brought on by excessive consumption of drink as soon as work lets up for the holidays.

3-: From the following message, posted by ‘Port Erin’ on Tuesday 16^th December 2008 on Manx Forums—A Discussion Board & Classifieds for the Isle of Man:

A traditional Manx event is taking place this Friday in Douglas—‘black eye Friday’, as the Police fondly call it.
This is the last Friday before Christmas, everyone has been paid, a lot of people break up for the festive season and mark the occasion by getting hammered and knocking 7 bells out of each other.
All Police leave is cancelled—let WW3 begin.

4-: From The Cumberland News (Carlisle, Cumbria, England) of Thursday 18^th December 2008:

CUMBRIAN POLICE BRACED FOR BLACK EYE FRIDAY
By Chris Story
Last updated at 20:11, Thursday, 18 December 2008
EXTRA police will be deployed across Cumbria tomorrow as pubs and clubs prepare for one of their busiest nights of the year.

5-: From Isle of Man News, published on Friday 19^th December 2008 on 3FM: The Isle of Man’s feel good radio station:

‘Black Eye Friday’
Friday, 19 December 2008 08:50
Police chiefs say they’ll take a hard line on anti social drinkers tonight.
Extra officers will be out and about across the Island to tackle and deter any potential problems.
For many today is the last day in work till the New Year, it’s also last day of term in schools.
It’s been nicknamed ‘black eye Friday.’
The police are hoping people act responsibly.