This is one of my favourite internet discussion topics.
0 F ~= -18 C, which is pretty cold but not terrible. And in that image above, where 0 C was "fairly cold"? Ha, no it's not.
Depends on where you live. As someone who's grown up in the northeast US, I agree. 0C is not that bad, but you're still wearing a jacket. I spent some time in Atlanta for work - and laughed my ass off when people were wearing fur hats to work when it was 50 degrees (F) outside.
If you really wanted to define the scale based on human safety, I'd probably go with -20F -> 0 Degrees Frisk, and 120 degress F -> 100 Degrees Frisk.
It was this discussion that actually caused me to look up how Fahrenheit came up with the scale. Pretty interesting read. He basically defined 3 points - the temperature of a brine mixture, the temperature of icewater, and human body temperature. He used brine as 0, and then defined the difference betwen ice water and and human body temp as 64 degrees because it was a power of 2, so it was easy to bisect the differences in powers of 2 on his scale.
It's just a fortunate co-incidence that the helps in conversationally discussing the temperature of things you can touch.