I can carry on a conversation about American healthcare and foreign policy for hours, and then a PEZ candy comes up and I look all lost and shake my head, asking "What is PEZ?" The usual reaction is "C'mon, you know what PEZ is, you're just joking, right?" No, I was not.
Another episode that comes to my mind happened shortly after I moved here. A girl was telling me about this famous singer, who all boys had a crush on and most girls wanted to look like. I put my smile on and was nodding in agreement having no clue who we were talking about. Not because the singer is not popular, just because she's not that popular in my country and I normally don't listen to that kind of music. That singer's name was.... Taylor Swift. Ok, you can laugh now, I realize how shockingly ignorant I must have looked then not knowing who the princess of country music was.
So don't be surprised if someone tells you they never had marshmallows, peanut butter or played with yo-yo in their life. As unbelievable as it may seem to you, many things in the United States are not global-wide and universal :)
And here some other references most foreigners have not heard of if they've never been to the states:
Mike "The Situation"
Shocker, I know.