While the rivalries between Ireland and England (well, everyone and England), Dublin and Kerry, and Manchester United and Liverpool have been going on since time immemorial, there are other rivalries which have sprouted in modern times, fed by circumstance and revealed through online activity.
Here are just three rivalries have acquired added spice in the modern era (including one which many regard as much older than it is). These are grudge matches that have only earned that title in modern times. Any more you can think of, let us know.
Ireland v Wales
In the early days of professionalism, the Ireland v Wales fixture tended to decide the destination of the wooden spoon. For whatever reason, the away team would usually emerge triumphant. Between 1984 and 2001, only twice did victory go to the home side. Despite the high(ish) stakes, the match-up never received the same billing as the Ireland-England game.
These days, the Ireland-Wales match often decides the destination of the Six Nations championship. Between them, Ireland and Wales have won six of the past eight titles. The even higher stakes may have served to inject some serious spite into the fixture.
One sees it in forums, where posters often declare that they now enjoy beating Wales more than England. The personage of Warren Gatland is influential in this new mood.
The perception in Ireland is that Warren can't pass a microphone without needling the Irish in some unsubtle way. By all (Irish) accounts, this is a consequence of Gatland's soreness at his abrupt sacking by the IRFU in 2001.
In advance of the Grand Slam game in Cardiff in 2009, Gatland told the pressmen that his squad disliked the Irish players more than any other Six Nations side.
The following day, he clarified this remark, saying he intended it as a compliment to the Irish. The Welsh players had been humbled so often by the provinces in the Celtic League, there was bound to be some antipathy.
Relations had hardly cooled by the time of the 2013 Lions tour. In the intervening period, Wales had gained the upper hand in the relationship. They defeated Ireland in the 2011 Six Nations, by virtue of one of the biggest refereeing howlers in the competition's history.
Their fans and players were unresponsive to Irish complaints, referring to usually unspecified incidents of Irish good luck in Cardiff down the years. The most recent anyone could cite was a dodgy try scored by Paul Dean in 1989.
Gatland's dropping of Brian O'Driscoll firmly established Wales as a modern enemy to rival England.
2015 perhaps represented the high-water mark of the Ireland-Wales rivalry. Neil Francis remarked that Warren's intellectual prowess was equivalent to a tub of margarine. Living in a country that often fixates on what foreigners have to say about us, it was gratifying to realise that there is a neighbouring country that is even more sensitive.
The Welsh went nuts about Francis's hyperbolic insult. Backs coach Rob Howley and columnist Carolyn Hitt condemned Francis, while Tony Copsey indicated he might be willing to give him another slap. On the day of the match in Cardiff, the Western Mail's front page consisted of a plea to the Welsh players to shut up 'cocky Irish pundits'.
Even the recent World Cup, where Ireland and Wales didn't meet, presented evidence of this spiky new rivalry. Those of us charged with scouring twitter feeds and online forums will have detected this easily.
In the aftermath of Ireland's exit, Welsh commenters were disproportionately prominent among those protesting the narrative that Ireland had lost out due to their crippling injury crisis.
Kerry v Mayo
The added frisson that currently exists between Kerry and Mayo supporters, easily detectable online, can be traced back to August 31, 2014.
While the two teams have duelled frequently in the modern era, the one sided nature of many of the games precluded the growth of any spite between the two sets of supporters.
By 2014, Mayo fans felt they had Kerry's measure, and thus found the semi-final loss especially hard to stomach.
Mayo were already annoyed at the choice of venue. Unlike them, Kerry were not strangers to the Gaelic Grounds. During the game, they were incensed by Cormac Reilly's contentious refereeing performance.
Finally, it was the cynical manner in which Kerry closed out the game that tipped many Mayo supporters over the edge. That, this was standard behaviour for all teams defending a lead late in the game was ignored.
No county's supporters are more energetic when it comes to online activity and they turned their guns on Kerry in the immediate aftermath of that game. Rarely has a result been greeted with such outrage on Twitter. They were a long time getting over it.
Over a year on, it is our view that they haven't quite forgiven them.
Leinster v Munster
Eyebrow raising? Hear us out.
The Leinster-Munster rivalry as a mass spectator phenomenon is a much more recent development than most modern rugby fans realise.
Watching the fervour of their supporters these days, it's easy to think that the red hordes have travelled to Munster games in their droves since the early days of the oval game. The truth is that Munster's success in the modern era pre-dates the bulk of their following jumping on board - not the other way around.
The inter-provincial championship, which was discontinued once the Celtic League was introduced, proceeded every December and inspired widespread disinterest. It was an unloved competition, especially down South. That Ulster dominated the tournament in the '80s and 90s didn't help in this regard.
In those quaint pre-professionalism days, Munster games against Leinster attracted miserable crowds. A few hundred battered veterans would troop out to Dooradoyle or Thomond each December but no more than that.
Back in the early 90s, it was all about the AIL.
Indeed, as Prof. Liam O'Callaghan has noted, Limerick in particular was hostile to the idea of Munster rugby in those days. There was a belief that the selectors of the provincial side routinely favoured posh Cork boys ahead of their own local heroes.
The Leinster bandwagon was even slower to grind into gear. By the mid noughties, it was still something of a cliche that every county in the province outside of Dublin was at best neutral on the Leinster-Munster question.
While there were significant matches like the inaugural Celtic League Final, where fourteen man Leinster somehow beat the then more fashionable (if that's the right word, which it isn't) Munster in Lansdowne Road, it wasn't until 2006 when the rivalry really kicked into gear.
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