The North West cities of Liverpool and Manchester have held a rivalry since their battle for supremacy in the industrial era and, with Sir Alex Ferguson in particular having fired things up on the football side, the enmity between the clubs has grown and grown.
Ahead of Sunday's Premier League meeting, ESPNsoccernet selects the First XI flashpoints between the sides in recent decades.
Ferguson sees Red - 1980
There's little doubt that Ferguson has played a significant role in ramping up the rivalry between the two clubs, but it's said that his bad feeling for the Reds actually pre-dates his arrival at Old Trafford in 1986.
Ferguson's Aberdeen side suffered a rude awakening in the second round of the European Cup in 1980 and, before the first leg at Pittodrie, Ferguson said: "Obviously, this is the biggest thing for Aberdeen since the discovery of oil. The fans see it as a straight Anglo-Scottish battle. Liverpool are not unbeatable."
The Dons were, however, beaten 1-0 in the first leg courtesy of Terry McDermott's goal, which came while John McMaster lay injured. The midfielder suffered ligament damage as a result of Ray Kennedy's tackle and then spent the next 18 months on the sidelines.
If that was not enough to spark Ferguson's ire, his side were then comprehensively outclassed in the second leg at Anfield, losing 4-0, and Reds boss Bob Paisley mocked the visitors afterwards. "If it had been a late kick-off, I'd say we played brilliantly," he said. "I thought the players were selling newspapers in the first half hour. They made Aberdeen look better than they are."
'Choking on their own vomit' - 1988
Having seen Colin Gibson sent off in a 3-3 draw at Anfield, Ferguson complained that visiting managers "have to leave here choking on their own vomit - biting on their tongue, afraid to tell the truth". He added: "To win here, you have to surmount a lot of pressure, a lot of obstacles and, if you want to blame the referee, you can't say so. The provocation and intimidation he is under are incredible. To win here is a miracle."
Given Liverpool's undoubted superiority at the time, Kenny Dalglish was able to resist the mind-games and, holding his baby in his arms, replied simply that the media "would get more sense out of my six-week-old daughter, Lauren".
They were not Ferguson's only comments in that period to suggest he was determined to remove Liverpool from their throne. In August 1988, he warned that life would "change for Liverpool and everyone else - dramatically" when he fulfilled his "mission" with United, while little over a year later, he warned again that he was "not going to accept Liverpool's dominance".
Dalglish snaps - 1994
While Dalglish, a very private man, may have convinced the public he had no quarrel with Ferguson during his Anfield days, some of that composure was lost during his time at Blackburn.
It's been claimed that the duo rowed furiously when, following the news that his friend Alan Hansen had been dropped, Dalglish pulled out of the Scotland squad for the 1986 World Cup through an apparent injury. It's said they rowed during Aberdeen's European Cup thrashing at Anfield six years earlier, too.
As rival managers, there was a story that Dalglish swore at Ferguson in a confrontation during the aforementioned 3-3 draw in 1988, but the Liverpool boss threatened a libel action against the newspaper that published it. He was also said to have criticised Ferguson in front of journalists around the same time, but he called a paper afterwards to label it "one incident blown up out of all proportion".
In 1994, though, when Dalglish was at Blackburn, the mask finally slipped. The usually reserved Dalglish, already riled after United signed Roy Keane from under their noses the previous summer, used a press conference in March to launch into what was described in The Observer as a "fearsome tirade against Ferguson and United, sarcastic and sneering". Among other remarks, Dalglish claimed "the people" wanted Blackburn to beat United to the title and that Fergie's suggestion Rovers would crack under the pressure was an "insult".
One of Dalglish's former team-mates, who wasn't named, told The Observer: "There was always the Liverpool-Manchester United thing, but nobody thought they had any time for each other." Another added: "We always felt he was particularly keen to beat Manchester United."
Phlegm and a flailing fist - 1996
By the end of the 1996 season, United were becoming firmly established as England's top side after winning their third title in four seasons and, thanks to an 85th-minute effort from Eric Cantona in the FA Cup final, they completed their second Double.
Liverpool's supporters did not react well to their side's abdication. As Cantona climbed Wembley's 39 steps to collect the FA Cup, a Reds fan spat in his direction and, worse, another supporter then attempted to punch Ferguson. FA chief executive Graham Kelly admitted afterwards that there was "a problem with players walking past rival fans", although Fergie joked that the fan "obviously doesn't know how good I am at fighting".
'Knocking them off their f****** perch' - 2002
In a 2002 interview with the Guardian, Ferguson finally admitted: "My greatest challenge was knocking Liverpool right off their f****** perch. And you can print that."
He has now come close to achieving that aim, having matched Liverpool's 18 league titles, but Jamie Carragher rejected Ferguson's claim to his greatest achievement earlier this month. "He never knocked Liverpool off their f****** perch," he said. "That's nonsense, that. Graeme Souness did that."
Rooney Kops a new phone - 2005
Wayne Rooney brought an extra dollop of hatred to the rivalry. In comments published on United's official website in 2009, he said: "I grew up an Everton fan, my whole family are Everton fans, and I grew up hating Liverpool - and that hasn't changed." United withdrew the remark the same day.
His feelings towards the Reds, though, had never been in doubt. On his first trip to Anfield as a Red Devil, he cupped his hands to his ears in the direction of the Kop having scored what proved to be the only goal of the game, causing one irate fan throw his mobile phone at him - prompting an arrest.
Gary Neville's thrusting - 2006
"I can't stand Liverpool. I can't stand Liverpool people. I can't stand anything to do with them." The embodiment of rabid mutual hatred between the clubs, Neville has put his own safety in jeopardy in defence of his right to badmouth United's arch-rivals.
After a group of Liverpool fans tried to overturn his car after spotting him stuck in traffic near Old Trafford, an unusually clear-headed Neville said during the 1999-2000 season: "I think I'm probably better off keeping my mouth shut about Liverpool from now on because I keep getting myself in trouble. I keep getting death threats."
His instinct towards self-preservation was seemingly forgotten by January 2006, when he reacted to an injury-time winner from Rio Ferdinand at Old Trafford by charging towards the visiting Liverpool supporters, thrusting his pelvis and kissing the badge.
Greater Manchester Police wrote a letter "expressing concern" that his actions had exacerbated crowd problems and he was fined £5,000 by the FA, but he remained characteristically defiant, asking: "Do they want a game of robots?"
Last week, though, Neville was striking a more conciliatory tone with the Reds in favour of his growing hatred for Manchester City. "I have more respect for their traditions than I would for some of the other clubs coming onto the scene throwing a load of money at it," he told MUTV, admitting he was "jealous" of Liverpool's success as a United-supporting youngster.
Ambulance attacks and a cup of poo - 2006
In February 2006, Liverpool fans attacked an ambulance containing Alan Smith with bottles, beer glasses and stones while chanting "Munich scum" in reference to the deaths of eight United players half a century earlier. Ferguson said Smith, who has never been the same player since breaking his leg and dislocating his ankle that day, had some of the worst injuries he had ever seen.
It also emerged that United fans had written to Liverpool after the game to complain that they had been pelted with excrement during their trip to Anfield. Liverpool stadium and operations manager Ged Poynton subsequently admitted: "We hold our hands up as a club. We deplore what certain fans have done. I am ashamed to admit in one case excrement was thrown. How low can you get? We did what we could. We tried to brush people down and compensate those involved."
Gabriel Heinze's letter - 2007
Once a terrace favourite, Heinze committed the ultimate sin in the eyes of the United fans in 2007 when he demanded a move to Anfield.
No player has crossed the divide since Phil Chisnall headed to Liverpool in 1964, but Heinze invited the Premier League to help push the move through on account of the fact he claimed to have a letter from the United chief executive, David Gill, saying he could join any club that met his asking price. United stood firm and Heinze eventually ended up at Real Madrid.
'Facts' - 2009
Rafael Benitez developed a reputation for dull, non-committal answers in interviews during his time at Anfield, but the assembled journalists were in for an almighty shock when he arrived at Melwood, script in hand, to deliver a five-minute speech setting out myriad "facts" about United's stranglehold on the game.
Its message actually bore notable similarity to Fergie's own rant of 1988, but it has been most widely compared to Liverpool legend Kevin Keegan's "love it" meltdown in the 1995-96 season when Newcastle were battling United for the title.
Keegan's rant came at the end of a three-match winning streak for Newcastle, and they then drew their remaining two games to finish four points behind United. Liverpool, meanwhile, had beaten Bolton 3-0 and Newcastle 5-1 before Rafa's press conference, and they went on to draw the games that followed against Stoke, Everton and Wigan as they also finished four points adrift.
Fifteen Minutes That Shook the World - 2009
This comedy film celebrating Liverpool's 2005 Champions League triumph over AC Milan involved a couple of less-than-subtle jibes at Ferguson and Neville: whisky-swilling drunk 'McTaggart' becomes suicidal after the Reds' stunning comeback and one of his players, 'Rat Boy', sings a song about his hatred of Liverpudlians.
Amusingly, it wasn't merely a fans' project - Steven Gerrard, Jamie Carragher and Didi Hamann all made cameo appearances, while Rafael Benitez - who was portrayed by Liverpudlian Peep Show actor Neil Fitzmaurice - went along to the premiere, laughed hysterically throughout the screening and then apparently continued to chuckle his way through some post-film interviews.