I'll bite (and I grew up in one of the colder parts of Canada, so I'd call 0F a cold but not unreasonable winter day).

-30: Avoid going outside, if you do don't leave any exposed skin

-20: A cold winter day: toque, scarf, mittens, winter coat and boots are must have

-10: An average winter day: same load-out as above, but you'll be more comfortable

0: A mild winter day: snow possible, you may leave your winter jacket open, or skip the scarf

10: Early spring or late fall: you might be able to get away with a light jacket, but I'd leave that until 15

15: Long pants and light jacket

20: Leave the jacket home, maybe wear shorts or a t-shirt

25: Comfortable summer weather: shorts and t-shirt

30: Annoyingly hot summer weather, good for swimming

35 or higher: hole up somewhere with AC

LOL. I'm in Western Australia:

<10: Bloody cold, avoid going outside if possible. Rug up if you do.

15: Winter. Probably rain and wind.

20: Cool Autumn / Spring, you might need a jumper outside.

25: Vaguely warmish, t-shirt weather.

30: Getting warm, wear shorts and t-shirt.

35: Beach weather, avoid going outside for too long if you're in office attire and don't want sweat patches.

40+: Hot beach weather, stay out of the sun (or in the water) in the middle of the day.

Interesting...I'm in the UK, for me 24°C with a light breeze makes for a perfect Summer's day: warm enough to walk around without sweating buckets. 30°C is uncomfortably hot. I guess it's all relative to what you're used to (and what you're doing e.g. day at the beach or walking in the city).

Well, people don't for the most part look forward to 40 degree days - this is warmer than body temperature, so you have to engage in some form of cooling. Going to the beach is one form of cooling :) Avoid being outside, drink lots of fluids, AC if you can, anything, really. Construction workers generally stop work around 36, from memory. Conversely, people here will tell stories about the crazy British neighbour who is out doing the gardening in a singlet when it's only 10 degrees.

Here in Melbourne we'll have several 40-degree days each summer, and the only large city with more that I'm aware of is Phoenix. There are heaps of large cities that are warmer in general, but they don't peak quite as high. Record is 46.2, set a few years ago. Not a pleasant day, especially since it was after a few similar days...

Victoria, Australia here. About the same, except we can get three or four of those all in the one day. (The running joke is that if you don’t like the weather in Melbourne, wait.)

I’ve lived in both the low and highlands of Papua New Guinea and they have two types of weather: dry and wet. In the lowlands you do not go outside without wearing a hat as the sun will actively try and kill you. When a PNG friend visited us in Melbourne, it was a 30°C day, we were in shorts and t-shirts, he was in jeans and wearing a parka to keep warm.

Canadian here as well I see some people in shorts at 10C maybe even at 0C mostly "dudes" in their 20s and late teens. I even see bigger (fatter) guys in shorts in the middle of winter now it seems to be a thing.

After a cold winter 0C even -10C feels warm especially if there isn't any wind.

I don't know anyone who zips up their jacket unless it's -15C or -10C and windy.

It's the wind that gets you, -20C is nothing if there isn't any wind.

But really it also depends a lot on perspective since 10C in the spring feels very warm but 10C in the fall feels very cold. Maybe a lot of the descriptions depend on year round average temperatures, I can image people in southern California with a smaller temperature range would not feel as much of a difference as a Canadian would.

Not bad.

As a Brit:

-20: Inside a food freezer.

-10: Ski trousers weather. Doesn't happen where I live.

-5: There'll be snow, or at least frost. Hat & gloves weather. Happens one or two days a year.

0: Freezing, usefully. Full-length coat.

5: Pretty cold - not unusual for a winter day. Fridge temperature. Don't forget your jacket.

10: A warmer winter day, or typical early spring.

15: Spring/Autumn; temperature where I'd stop bothering with a jacket.

20: "room temperature" for science (though many actual rooms are a degree or two higher than this). Comfortable.

25: A sunny summer's day. Pleasantly warm.

30: Starting to get towards uncomfortably hot. Notwithstanding this year, I'd only expect a few days this warm in a year.

35: Doesn't happen where I live. You want to be in the pool or somewhere with AC when it's this hot.

40: On a person, serious fever.

60-70: Nice for a sauna. Warm drink (e.g. tea)

That's pretty much it, except 90C sauna is quite decent.