VERY generally speaking, 20s are warm, 30s are hot. Humidity changes this a lot. And yes, personal sensitivity to heat plays a role. I live in a dry climate, and I feel rather comfortable until we’re close to 30 ºC. I remember reading something like the ideal room temperature for humans was around 20-22 ºC.
For those using F, this is, more or less, the scale of C:
Below 0: freezing (0 ºC being the freezing point of water, duh!)
0 to 10: cold (don’t go out without a coat)
10s: cool (a sweatshirt or light coat may do)
20s: warm
30s: hot
40s: uncomfortably hot (stay in the shade and hydrate)
50s: you’re dead (or you wish you were. Unsafe for humans)



Well… I said VERY generally speaking. And as I’m defining a gradient of temperatures (clearly it’s not the same 30 °C than 38 °C), I’m also defining a gradient of “hot” sensations, from feeling a bit of heat in your body, to feeling like an oven. That’s the thing with generalizations. I’m not trying to be precise here, just give a general idea to those that are not used to Celsius (I’ve seen the same being done with Farenheit and found it useful). Cheers.