Well... a person can't just go NC with everyone who's demanding or controlling in this world. But I do agree with the idea that a simple "no" can be quite powerful.
Here's the thing that bugs me: the former "doormat" is being advised to be controlling, manipulative back... which is the classic power struggle setup. No one "wins" in those - everyone loses...
Another way, is to look for a solution between the obvious choice of "either" and "or"... and try that instead. Part of me believes that my life would be glorious - a total dream - if I didn't have to maintain a connection with my brother through the business. That's a false illusion and I know it. He is still P-A and still doing wack things like asking me to go through a contract, page by page with him and tell him where to sign... but, it's not setting me off into frustrated spirals of triggered "violation" anymore (or hasn't recently). He insists on being this way... it is the way he is... for whatever reason, and I'm not going to change it. So I just change me - I take that kind of behavior off my "outrageous" list... and if I have something else to do I just tell him that means I can't be available to him, let him figure it out for himself -- or ask someone else. And it's not a trespass of any of my boundaries anymore... and it's not gasoline, either.
Am I always able to do this? NOPE, not by a long shot!! But I keep trying to remember to try this - because it's already too hot to get emotionally wound up, too.