alt text
Comic strip of a ghost and a person with the American flag pasted on the head. The ghost repeats "Boo!" in the first three panels without getting any reaction, but when it in the fourth panel says "kg, cm, km, °C" the American gets scared and screams "AHHHH!!!".
Edit: fixed alt text
3 actually, and it's not a good group.. And I'd like to say that most Americans actually support the idea of switching, but as a stubborn guy who uses metric for everything here I can sadly say that they are not by a long shot.