Living under a rock

If you are 'living under a rock,' it means that have not been paying very close attention to what's been happening (especially in the world) around you.

Example:
-I just can't comprehend how anyone could be an undecided voter at this point!
-They must be living under a rock!

Living under a rock

To say someone is 'living under a rock' means that they have not kept up with current events, trends or beliefs because they have kept themselves isolated or simply don't care. It is pejorative.

Example:
-Can you believe he still thinks it's okay to beat your children?
-What rock has he been living under?

Slept like a rock

If you 'slept like a rock,' it means that you had a great night's sleep and feel well-rested.

Example:
-How did you sleep?
-I slept like a rock! I feel great!

Between a rock and a hard place

If you're 'between a rock and a hard place,' it means you're in a difficult situation with no good way out. No matter what you decide to do, there will be negative consequences to your actions.

Example:
-I can buy groceries and pay my bills this month, or I can refill my prescriptions.
-You're definitely between a rock and a hard place.