I grew up in Singapore where people were practically always impatient. (Can't speak for now, as I left in 1974.)
I used to put this down to the weather: it's not easy to be placid and calm when you're hot and clammy all the time. (Average temperatures high 20s to low 30s; humidity around 80% most of the time.)
In my childhood days, drivers would honk impatiently at people crossing the road if they didn't quicken their pace at the sight of the approaching vehicle, as if the drivers had priority by right.
Drivers would hoot at the first vehicle at a set of traffic lights if it didn't shoot off as soon as the lights turned green.
In my early days in London, I'd witnessed the opposite on more than one occasion. The first driver at the lights hadn't even had his/her first gear engaged, ready to charge off when the lights turned green (which was what was expected in Singapore in my childhood days). The other drivers would patiently (and quietly) wait for that first driver to get the car into the first gear and move off. I was very impressed at how civilised people were. (Not anymore, I must add, from what I've seen in recent years. People are starting to behave badly.)
I'd always put it down to the weather in both cases (Singapore and Britain).
Some generalisations here from my own experience to support my weather theory (yes, Valerio, generalisations, but from my own experience): people from Mediterranean countries are much more excitable than Scandinavians who are calmer and more softly spoken.
However, a student once complained to the co-ordinator about my moving the young man next to her to another seat because she kept talking to him in class while the teaching was in progress. She said, "My Latin temperament doesn't quite get on with her style." (No, she's not Italian.) So, even she herself acknowledged that there's such a thing as temperament (or disposition).
Therefore, it's not just the weather, although the hot and humid weather must make the blood boil more quickly as well. It must be the temperament of Singaporeans (in my childhood days anyway) as well.
(Singapore, 1960s–75; UK, 1977 onwards)