I’ll go first: “You have to have children when you’re young,” told to me when I was in my late 20s, with no desire to ever have kids, and no means to support them, by someone divorced multiple times with at least one adult child who does not speak to them.
Also: Responding to “How do I deal with this problem?” questions with “Oh, don’t worry about it, it’s enough that you’re even thinking about it!”
I always tell them “Following that logic, there’s only one person in the world that can complain. But that dude really got it bad.”
My counter is always, “and there are people better off than you, so stop being happy.”