Would make an interesting topic.
Personally I always thought Rangers edged it with their fans embarrassing pro English pish, (with the anti-scottish vibes to it) over the years. Even way before the liquidation and cheating.
St George flags in the crowd etc. Never quite got all that. I remember them singing "we'll be watching england, so will you". This to me was a giant two fingers up and a laugh at our national team.
Thrown in the nazi salutes etc and...well they may be one half of the same arse, but their half has giant festering boils on it.
Celtic are a bit easier to swallow for a lot of Scots I reckon. Siding with Ireland is a lot more digestible to the average Scot than worshiping the English to a ridiculously extravagant level. Thats just my take though.