(although, got to say, peanut butter and jelly is a combination I cannot fathom)
Until about two years ago, I couldn't fathom that anyone would not know of peanut butter and jelly. To me, it's the epitome of a pair that always goes together (I mean, I use jam instead of jelly, but still). Then my brother found out that no one he met in Japan had ever had the combination. All his Japanese friends tried it and agreed they tasted good together, but they probably wouldn't combine them just because they're not used to it.