Real-world idioms: "He would be turning over in his grave if..."
I heard this the other day. It is a familiar idiom in the United States. The exact wording varies. It can be "he would be turning over in his grave," "rolling in his grave," or "spinning in his grave."
It means that someone who is dead would not have approved of something that's happening. Literally, the phrase suggests that the person is not "resting in peace." He is tossing and turning in his grave, like a restless sleeper.
It is often used in a joking way. It often means that standards have changed, and that the speaker accepts something that the dead person would never have accepted.
Examples:
"Your grandfather would be turning over in his grave if he knew that you decided to attend Cal Tech instead of Princeton."
"Your grandmother would be rolling in her grave if she knew you were getting a tattoo."
It can, however, be used very seriously. For example, it can mean that someone has betrayed the ideals of a former leader. "[That leader] would be turning over in his grave if he knew what [his party] is doing now."