Graphite, you make excellent points on how wearing a wrong football top in the wrong city, anywhere in the world can get you 8n deep shit.
Thanks I come from a Celtic supporting family but a few have married rangers supporters. I'm not really a footy fan myself but I'm well aware of the issues & tensions around certain teams. Old firm are known for it and the tensions aren't just due to footy rivalry but other socio-political factors I'm sure readers are aware of its complicated (but equally bloody stupid!) but it's true of others in uk too.
My ex supports a team infamous for having fans who are troublemakers, and with an infamous Derby rivalry with a club with a similar reputation!
He also has whatever the male equivalent of "resting bitch face" is so he's had people having a go cos they think he's giving them dirty looks, in addition until recently he was army so he's quite muscular and army hair regulations made him stand out at times, so he went/goes (as far as I know) to home matches when he can but is selective which away matches he goes to and never goes to derby matches as he learned early on he just gets grief!
He has friends that are supporters of the other team and they good naturedly rib each other about the other team being crap, especially of course if there's just been a match and the losing team has to take the shame, but these are people he's known since school and it's not serious. One guy did go too far once and ex & the others cut him out as a result but he was a dick in other ways too and I suspect it was a "last straw" thing.
But I've even family & friends in USA and even there - where they claim their big sporting events are "family friendly" - I've heard stories about people getting battered for going in the "wrong" bar where the bar's full of defeated fans, and the twit's wearing the winning rivals shirt! (and sometimes also gloating but not always)
Happens the world over.