That's racist that pal and for your info Croats aren't Slavic, its just that their language that is. Much like the Irish aren't German despite speaking a Germanic language.
Racist? You sure? South Slavic include the Bosniaks, Bulgarians, Croats, Macedonians, Montenegrins, Serbs and Slovenes. They are the main population of the Central and Southern European countries of Bulgaria, Bosnia and Herzegovina, Croatia, Republic of Macedonia, Montenegro, Serbia and Slovenia.
To suggest that folk from those nations like a flare or 5 is hardly racist. Flares are common place in most sports stadia, I've seen them at MMA, Football, Down hill skiing, basketball even tennis for fucks sake.
If you're trawling the Internet looking to accuse someone of racism, I wouldn't start with someone calling a Slavic speaking nation with southern Slavic heritage 'Slavic'.
If you take issue with me suggesting that flares are common place in Southern European and Slavic regions in the sporting arena then that's sterotyping not racism.
I'm sure there's someone somewhere suggesting the Scots and the Irish like a drink, the Brits burn in the sun, Russians like a vodka, Germans like to pop a towl out early and American's are hot dog eaters that you could falsey accuse.
You're a clown and accusing someone of racism is pretty fucking low. Especially when you're wrong.