Going a bit off-topic here, but as a tiramisu lover I feel compelled to say that if you like desserts and coffee, generally, you might consider trying some if the opportunity presents itself.

A bit more on topic, I'd generally agree that it's not so common as to be universal. I don't think I'd heard the word in any way that registered as significant before my mid-20s, and I'm certain I never tried it until my late 20s or early 30s. I grew up in the suburbs around Pittsburgh, PA with plenty of passable Italian restaurants -- but tiramisu simply wasn't a dessert people in my family ordered.