Only in Johto, Unova, and occasionally Kalos. (Alola as well, but for them, it’s less an accident and more a cultural point.) No one is quite sure why, but the going theory is that the starters often emulate the disposition of the people within their region of origin.
As a Johtonian, I feel like I should be offended by the implication that my people are all impulsive and extremely transparent about their opinions of others, but on the other hand, you wouldn’t exactly be wrong if you said that…