I live in New York, which has a basic culture of "hyper aggressiveness." It isn't "rudeness," as so many people like to think of New Yorkers. They can be aggressively kind and generous. They are just aggressive.
I'm also in the tech industry, which seems to have a very aggressive and competitive culture.
It doesn't stop me from being kind and courteous, but it gets grating.
My experience is that, when someone mistakes courtesy for weakness, they start trying to "game" me. I put up with it for a bit, until they push too far.
Then the till gets slammed on their fingers.
They get very, very upset. Far more upset than if I had just disabused them early on.
I'm learning to enforce my boundaries earlier. It doesn't make me as popular, but it also prevents those "psycho freakouts."