One that comes to mind for me: “Whatever doesn’t kill you makes you stronger” is not always true. Maybe even only half the time! Are there any phrases you tend to hear and shake your head at?
I mean, everything does happen for a reason. It’s just that most of the time, the reason is “because so-and-so is an asshole”. It makes it essentially a useless platitude, but not an untrue one. I definitely take issue with the implication of it, that there’s some supreme, all-knowing authority in the universe who has this complicated, labyrinthine plan for everyone that involves massive amounts of suffering. That whole “mysterious plan of God” thing is a way for Christians to take credit for all of the good stuff that happens, while downplaying all of the bad stuff that happens as just “part of God’s plan!” It’s insidious.