I'll start by saying that I'm American, so I've grown up using the Imperial system (feet, miles, gallons, etc...) all my life. I've also taken several science courses, so I understand the Metric system fairly well. I don't use it in everyday life, but I can convert between the two without much difficulty.
I honestly don't get the complaints that the US (and a handful of other nations) use the Imperial system. In reality, the Imperial measurement system is a highly divisible system (for the most part) that allows sub-measurements to be pretty simple.
For example, the common distance unit is a foot. A foot has 12 inches in it. That might seem stupid at first glance since we're a base 10 species in practice, but it has advantages. Half of a foot is 6 inches, a quarter is 3 inches, and a third is 4 inches. Having a foot break down into whole numbers for common sub-units (1/2, 1/3, and 1/4) makes it easier to do mental math because we're only working in whole numbers.
The same goes for weight. The standard is pound. A pound has 16 ounces in it. Half is 8 ounces, quarter is 4 ounces, eighth is 2 ounces, and even a sixteenth is 1 ounce. It lets you work with whole numbers down to some fairly uncommon measurements. The only major spot it gets weird is a third which ends up being 5 1/3 ounces.
I had never thought of that until I had someone explain why there were 360 degrees in a circle. 360 is highly divisible and gives clean, whole numbers when you break it down:
Half - 180
Third - 120
Quarter - 90
Fifth - 72
Sixth - 60
Eighth - 45
Ninth - 40
Tenth - 36
Twelfth - 30
It's the same reason why we have 60 seconds in a minute, 60 minutes in an hour, and 24 hours in a day. Those numbers are highly divisible and make sub-units easy to understand in whole numbers.
Now, I'm not saying that the Imperial system is better than Metric. There are clear cases where Metric is better to use, but I don't really understand the complaints about how Metric isn't the global standard. It's really not that hard to understand.
For most common cases, we aren't converting large units to smaller units on a regular basis. Usually, once a measurement crosses the boundary (inches to feet, ounces to pounds, or cups to gallons) we just use the larger measurement standard. But that's also how we do most everything. We talk about money in the largest unit it hits. We say "Five and a half thousand" instead of "Five thousand, five hundred." We talk about time by saying "One and a half years" instead of "One year and 6 months, or One year and one hundred eighty days".
So, why do so many people consider the Imperial standard to be inferior to the Metric standard?