People who have grown up in the North know "the rules" that go hand-in-hand with supporting a Scottish football team.
If you were raised in a Catholic area you are supposed to support Celtic, and if you were raised in a Protestant area you are supposed to support Rangers.
It is as basic, simple, and ridiculous as that.
Depending on where you were brought up, e
ither Rangers or Celtic - and their fans - are supposed to be your natural enemy.
Thankfully, I grew up with zero interest in Scottish football. Growing up in the Waterside, my folks must have been grateful that I didn't insist on getting the latest Celtic kit with Paul McStay's name splashed across the back.
During my teens, I realised that supporting either Celtic or Rangers is ample enough reason for people to pick fights with strangers.
It is also a thinly-veiled (or completely "unveiled") excuse for sectarian violence and bigotry.
There has always been rivalry in football, but the Old Firm divide incorporates political, cultural and religious differences more than any North London or Manchester derby ever could.
As recently as the end of last month, Celtic goalkeeper Artur Boruc wound-up Rangers fans when he revealed a t-shirt emblazoned with the slogan 'God Bless the Pope' and a picture of the late Pope John Paul II after a game.
East Derry MLA - and avid Rangers supporter - Gregory Campbell deemed the gesture, in a 'fairly hostile environment', inappropriate.
There have been tit-for-tat wind-ups over the years on both sides, most notably Paul Gascoigne's flute playing skit and Andy Goram's decision to sport a black armband following the death of Loyalist paramilitary, Billy Wright.
Refreshingly, there were photographs in the press this week of true football fans who were ready, willing and able to rise above the foolish sectarianism and pay tribute to the life of Tommy Burns, who died last week aged 51.
During his career, Burns played for, and managed, Glasgow Celtic.
He was also involved with the Scottish national team and, following his death from skin cancer, there was a huge outpouring of grief from both sides of the Old Firm divide.
An estimated 3,000 mourners stood outside St Mary's Church, Calton, listening to his funeral service which was led by more than 40 priests and two bishops on Tuesday.
More than 20,000 people gathered at Celtic Park in Glasgow to hear a broadcast of the funeral Mass.
The current Rangers captain, Barry Ferguson, is a figure of hate for many Celtic fans. That, presumably, is because he is the embodiment of all things "Rangers".
A 'local boy done good' he grew up in Glasgow, supported Rangers as a child and is currently the club's leader and most influential player.
'Mark of the man'
Ferguson knew Burns from their time together with the Scotland squad but there was a link between the two from before then.
