Because the Celtic fans would shit themselves and reply: "BUT WE ARE IRISH". Even though Great Britain does not equate to United Kingdom, Celtic fans are an irrational bunch and it would mean the same thing to them. In the real world Great Britain = Landmass United Kingdom = Every country in the Commonwealth (Australia, Canada, England, Wales, etc) In the Celtic world: Great Britain = Evil English Imperialists repressing humanity United Kingdom = Evil English Imperialists repressing humanity A Celtic fan once called me an Ignorant Evil English Imperialist because I told him I'm an Australian with English heritage...