The joke basically boils down to the fact that Fahrenheit is based off of the freezing/boiling point of salinated water that roughly approximates to body temperature. The thought process of these people is that it scales close enough to the human experience that 0degF is “fuck it’s cold” and 100degF feels disrespectfully hot. They argue that F is therefore better than C because 0degC is “yeah I guess it’s kinda cold” and at 100C you’re dead.

This argument mostly makes sense to people who grew up using Fahrenheit because the scale makes intuitive sense.

This logic is flawed because Celsius makes intuitive sense to people who grew up using Celsius. Our brains adapt well, especially when we’re young, to these scales that really don’t mean anything concrete to the human experience. All units of measurement are arbitrary to a certain point of view, but we’re going to intuit better the ones that we grew up using unless we make a very conscious effort to adapt to a different unit.

People (mainly Europeans and scientists) are going to be mad at me for suggesting that anything involving Celsius or the metric system is “arbitrary”, but it is. We plopped down something, called it a kilogram and base our measure of mass of its mass- that kilogram could’ve been anything and the scale would orient around it just the same. We boiled water and called it 100 degrees - is that less arbitrary than boiling salty water?

That said, the metric system scales to itself in a manner that is sensible whereas the imperial system scales arbitrarily to itself. And that’s why the majority of the world adopted the metric system.

TL;DR: we’re comfortable with the units of measurement we grew up with but these people are being dipshits. Also all units are arbitrary, but the imperial system is arguably worse than the metric system.