For me personally “really really cold” starts below -30°C and crazy hot is above +30°C. It’s very subjective and outside of US many areas have climate where Fahrenheit doesn’t make sense at all.
maybe that's why its popular in the US? for most of this country the 0-100 range works quite well to describe the normal range of outdoor temperature. we seem to like 0-100 ranges, for instance speed in MPH works out nicely.. "over 100 MPH!" is a common expression for extreme speed drivers. school grades are often a value out of 100, etc. which makes you wonder why we don't prefer metric lol