AOG, that was exactly my point, there are black football hooligans but the stereotype is of the pot-bellied, shaven headed, heavily tattoo'd white man (which is why I chose football hooligan).
Fair play if you wouldn't be offended and saw the joke in it, as would I, however would you not find it understandable if some people were offended by that as it's essentially saying football hooliganism is a white thing, so anyone with different coloured skin will have to make themselves white to effectively portray the role.
Tinks, some people definitely are OTT, they look for problems where there needn't be one, which I think does a disservice to those who are genuinely offended when people do cross the line. Of these students, I think there's only one who could possibly have a point and even that's based on the context. Surprised you didn't say when people dress up as Mr T, that's a popular one and always looks good!