Scotland loath the English

I have no interest in Football and it escapes me that it is called the beautiful game but what I can not understand he the attitude of some Scotsman when it comes to the English . In Scotland they selling T shirts with "I support Scotland and any one else but England" plus many other such slogans, even Scotsman who live locally including my son in law loath the English Football Team. Is it because the Scottish very rarely qualify and the Scots feel sub standard I do not know, yet in Afghanistan Scots , English, Welsh and Irish fight and die together, our troops have done this for centuries. Some say its just the social outcasts who are like this but can you remember Andy Murray's outburst. My Friends in the Martial Arts World do not have the same narrow view so why the rest