For those who didn't grow up in America...Your favorite and/or the most confusing American English phrase?

My father and I emigrated to the US from London when I was 7, and I remember as a second grade student in Oklahoma CIty being very confused at times, about what everyone was saying. Sixteen years later, I speak American English like I was born here, and English English phrases sound strange. If you are not from here, what strikes you as funny (ha ha) or funny (strange)?