Not exactly sayings, but...
(1) "All anyone with cancer wants...", "I know we all appreciate (or believe or feel or whatever)...", and all the other variations of someone being convinced that everyone
in a certain category feels the same way. And it's even worse when the person saying it doesn't even fit into that category themselves.
Example: There's a thing about people with cancer floating around Facebook, saying basically that while most of us want all sorts of superficial stuff, all someone with cancer wants is to live another day. Oh really? And, at least in my experience, none of the people posting it even have cancer themselves. How dare they speak for me!
(2) "No one else [except those of us in a very specific situation] would understand." It sounds so "us vs. them" to me. Have we given up on the idea that people can empathize with each other, even when they haven't experienced the identical situation?
Edited to say, oops, I posted something very similar to (1) way upthread somewhere. Sorry 'bout that.