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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!!!".
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Everyone outside of America.
You're either trolling or a living embodiment of the 'Americans think the USA is the whole world' meme. Nobody outside of the USA knows how long a football field is.