A zebra doesn't eat apples
A zebra doesn't eat apples means you're being a complete idiot and need to stop acting like you're not.
You said you'd be here in five minutes. It's been an hour. A zebra doesn't eat apples!
You told me you'd pass the class. You failed. A zebra doesn't eat apples!
You said you'd help me move. You're still here. A zebra doesn't eat apples!