Practice saying this with me...

"That doesn't work for me."

Good.  Now say it again, this time with more confidence.

"That doesn't work for me."

No need to be snooty,  just calmly repeat:
"That doesn't work for me."

Repeat this line anytime somebody is presenting you with something that is stressing you out needlessly.

Someone recently suggested this response to me and it was an epiphany.  

If something doesn't work for me, I don't always have to do it.  There are some non-negotiables we all deal with -- necessities for our family or workplace.  If you don't keep certain bases covered your family will not survive and neither will your job.  Of course we all need to cover those.  But I'm talking about non-essentials that are others expectations that they place on  you, or ways of doing things that they are pushing on you that  stress you out and don't add value to your life or even shorten your life.

Just say, "I'm sorry but that won't work for me" whether it be today, or this week, or right now, or indefinitely.  You'll live longer, with much more joy