Who gets your best work?
If you reserve your best effort for the irritable boss, the never-pleased client and the bully of a customer, then you've bought into a system that rewards the very people who are driving you nuts. It's no wonder you have clients like that--they get your best work.
On the other hand, when you make it clear (and then deliver) on the promise that your best work goes to those that are clear, respectful and patient, you become a specialist in having customers just like that.
One of the largest turning points of my career was firing the client who accounted for a third of my company's work. We were becoming really good at tolerating the stress that came from this engagement, and it became clear to me that we were about to sign up for a lifetime of clients like that.
Set free to work for those that we believed deserved our best work, we replaced the lost business in less than six months.
Years ago, I heard the story of a large retail financial services company that did the math and discovered that fewer than 5% of their customers were accounting for more than 80% of their customer service calls--and less than 1% of their profit. They sent these customers a nice note, let them know that they wouldn't be able to service them properly going forward, and offered to help them transfer their accounts to a competitor. With the time freed up, they could then have their customer service people double down on the customers that actually mattered to them... grease, but without the squeaky wheel part.
No, you can't always fire those that are imperious or bullies. But yes, you can figure out how to dig even deeper for those that aren't. That means you won't take advantage of their good nature, or settle for giving them merely what they will accept. Instead, you treat the good guys with even more effort and care and grace than you ever would have exerted for the tyrants.
The word will spread.
[The other alternative is a fine one, if you're up for it... specialize in the worst possible clients and bosses, the least gratifying assignments. You'll stand out in an uncrowded field! The mistake is thinking you're doing one and actually doing neither by doing both.]