a piece of cake you cant eat
A piece of cake you can't eat is like a rich kid who says money is no object, but ends up broke and crying in a McDonald's.
You said this test was easy. I got a D. You said you'd help. You skipped class.
He said the project was a breeze. I worked all weekend. He said he'd help. He was asleep.
She said the cake was delicious. It was soggy and tasted like regret.