The metric system
Oh no, this can be a sensitive topic for Americans, who are one of the only countries on the planet that still use the imperial system of measurement. They are actually well-known around the world for measuring things by feet and miles, instead of centimeters and kilometers. This can be quite a mess.

When they do collaborations with other countries in the realm of science or technology, this can actually cause some serious issues. They have to agree on which system they are using, or else when they bring their notes and findings together, it may not all add up correctly. Oh, they also measure things on football fields.