Reluctant to get into this but... I'm old enough to remember when it was celtic fans that were referred to us as Huns.
The Rangers end at Hampden and Ibrox used to sing 'the Huns are getting wet' as both their ends were uncovered. 'Go home ya Huns' was always a favourite as they started to leave the ground early in the face of a beating.
It was frequently sung in the 60s & early 70s & was applied given their support to the IRA and accordingly to Germany in the world war(s) when Eire was neutral & safe haven was given to U-boats.
I don't know why or how it was turned round & used to refer Rangers fans but it was.
I don't intend reciting the lyrics but they included "If I had a Tommy gun I'd shoot every F*n**n Hun, just for walking down the Queen's Highway"