Are you water? When is 100C ever relevant for you day to day?
Ahahah... When does water freeze or boil? At 0° and 100° Celsius. Much more convenient to remember those degrees rather than the corresponding Fahrenheit.
But it's obvious you're trolling. I, mean, I hope so otherwise it's sad. Because only a moron who has never cooked would ask that.
Where is freezing? That is a pretty important one particularly for driving or freezing pipes? So 40 is really hot, 20 is decent, 0 is freezing and -20 is cold and -40 is really cold. And water boils typically around 100.
I mean, ignoring zero in Calvin, it is all arbitrary when it comes to temperature. Just celsius likes to land some key numbers on human centric values.
You are talking purely out of ignorance. The majority of the population on Earth are getting on just fine using celsius with none of the problems you claim to exist.
Also "really cold" and "really hot" are purely subjective terms which varies a lot from person to person and from location to location.