I tell WBill Jr that "it builds character", whenever he whines about something. I may steal your idea, just to toss a changeup occasionally.
Take it with my compliments!
If you are looking for variety, you can say: “Life is hard, and then you die.” Gotta consider your audience - my boys both know Christ, so that means something good.
Another is from John Wayne: “Life is hard. It’s harder if you’re stupid.” That’s actually my favorite when I’m talking about whining democrats.