Who is liable if you borrow someone's car get into an accident and neither one has no car insurance?

Assuming that the driver of the borrowed car was At Fault, both the owner and driver can be held liable. The injured party will probably sue both. Whenever you borrow someone's car, ALWAYS demand proof of liability insurance before taking the keys because if this happens not only can you be sued but you might loose driving privledges until the injured party has been compensated in full, unless the person you hit had UNINSURED MOTORIST coverage in which case you'd definitely be off the hook but your friend's car would be siezed and auctioned by police for sure.