The first one was told by my mother.
When they were kids, children often quarreled. One day, Xiao Lan and Xiao Qiang got into an argument over something trivial. Xiao Qiang said: "I'm definitely stronger than you!" Xiao Lan immediately shot back: "You're strong, you're strong! May your 'strong' (wall) collapse and crush you to death!"
After hurling their insults, they both went home for dinner. That night, however, an earthquake struck (the 1976 Tangshan earthquake). My mother's hometown wasn't severely affected, but about twenty people in their village were killed—among them was Xiao Qiang...
Perhaps it was just a coincidence...
The second story was told by my roommate from Inner Mongolia.
It involved a quarrel between neighbors: Zhang family's pregnant daughter-in-law and Grandma Song.
I don't know what the argument was about, but anyway, the pregnant woman from the Zhang family shouted: "May you get hit by a car when you go out!" Grandma Song wasn't one to back down either and retorted: "May your baby be born without an anus!"
These are common curses people use during fights. But unexpectedly, in their case, these words came true...
The very next day, Grandma Song went out to buy groceries. As soon as she stepped out of her front door, she was hit by a motorcycle and died before she could even be taken to the hospital. (Hit by a motorcycle? I found that strange too!)
And sure enough, the Zhang family really did give birth to a son with no anus. They sought medical help everywhere, but nothing worked. The baby died within a few months.
This incident caused quite a stir at the time. My roommate's mother told her younger self: "In the future, when you curse someone, don't say anything so extreme!" (Though the implication seemed to be that cursing was still okay—just not *that* harsh... sweat.)