I suppose you are American, this isn't obscur for Europeans at all.
Am European, don't even know what a Six Nations Grand Slam is
Is it not? Does the average German or Portuguese or Finnish person know about the 6 nations?
I genuinely don't know. It's obviously a thing in Scotland (where I'm from) but is it a thing in other European countries?
I hear ya. I suppose the equivalent would be - last time the Chicago Cubs won the world series.