Three countries make up the Axis of Medieval (in refusing to adopt the metric system). The U.S. is one, but which other nations are willing to join them in brandishing their yard sticks and uniting against the world's most popular measurement system? It turns out their only allies in this fight are Liberia and Myanmar.
It's funny that while the U.S. has shunned the metric system in all other ways, it made total sense to them in terms of cash. Through the Mint Act of 1792, the U.S. became the first country to create a decimal based currency. Amazingly, the idea of setting 100 pennies to the dollar was novel for the time, especially since the dominant currency back then was the British pound/shilling/pence scheme which, at the time, set 12 pence to the shilling, and 20 shillings to the pound.
It's Illegal to discriminate against the metric system. Or at least it was. According to the Metric Act of 1866, the USMA reports that "This law made it unlawful to refuse to trade or deal in metric quantities." Please bring that up the next time you want to purchase a 2x4 (or rather, a 5.08x10.16) at Lowes.
Back when the whole Metric rage was taking place, the French decided to play with time as well. The Metric Calendar (also called the French Republican Calendar) divided the year into 12 months. While the 12 doesn't exactly fit into the scheme, each of those months was divided into three 10 day weeks. Each day was broken down into 10 decimal hours, and each hour was 100 decimal minutes each. While metric clocks and calendars were designed to push the new system, the idea never really took off, and mandatory use of the system was suspended just three years into its launch in 1795.
The metric becomes a problem in an episode of Archer, in regards to how much cocaine they have left:
Cyril: You will see that from our initial supply of 1,000 kilos of cocaine, we...
Archer: Hang on, dummy, we had a ton of cocaine.
Cyril: No, we... well, we had a tonne, that's T-O-N-N-E, also known as a metric ton, but...
Mallory: Metric. Who uses metric?
Lana: Every single country on the planet except for us, Liberia, and Burma.
Archer: Wow, really?
Lana: Yup.
Archer: Because you never think of those other two as having their shit together.
This culminates in Archer asking the value of their cocaine in:
Archer: No, I meant pounds—
Mallory: STERLING!
Archer: Exactly. As in Doctor Who money.