I rear ended a double parked car who left the scene what do?

Go grab a coffee and cool down.

How much damage was caused to both yours and the other vehicle?

You are liable for all damage so if the other driver has left the scene in their vehicle without exchanging details that's half the damage you don't have to worry about. If the driver has just wandered off and left the vehicle then you must take it's details and report the accident to the police and your insurance company.

If you've caused enough damage to your vehicle that it must be repaired then it's down to you or your insurance company to pay for.

So over your cup of coffee work out if repairs are needed and who you want to pay for them.

The fact that the car was double parked makes no difference, you cannot go around hitting stationary objects no matter where they are.

The other vehicle took off running, remember? That means you get to tell the story however you want.

Are you sure the other vehicle didn't back into you? Positive?

You drove into a parked car. Your fault.

Report it to the police and your insurance.

Then move on.

Hope that they don't return