Wait, is tiramisu really that common that everyone knows what it is?

I think you're expecting too much from others. I didn't grow up Amish, and although I did grow up in a non-assimilated insular religious community I've been living in Western secular society for about 10 years now.

The only Italian foods I can think of are pasta (I can name spaghetti and macaroni and lasagna and that's it) and pizza, which I knew of since childhood. Lately I've seen the word tiramisu around but I have no idea what it is. I think I saw it on a cake in a bakery and I assumed it was pretentious for chocolate but actually I don't know. I certainly didn't know it was Italian.