Is it legal to drive another person's car?

No, if one is not covered by an insurance policy, one may be cited if stopped. Thankfully, the law is permeable, so if one were to drive another's car in order to prevent public or personal damage, the police officer on the scene (if there is one) may elect to "let you go".

In addition, it is legal to drive another person's car if you have their permission. Depending on where the vehicle is insured, insurance policies have provisions for drivers who are not covered by the policy but who have permission from the owner to drive it.