I am dropping a regular customer that is not worth the trouble. If using a CC, I would just ignore any orders until they go away, but they use PayPal. Can I ban the acceptance of incoming funds from a specific email address? That would be easiest. Otherwise, I am just going to send it back.
I haven't seen any security features in Paypal to ban a email addy, Paypal should be able to let you know. You could also look into banning thier IP address from accessing your site it's not a sure thing as they could use a different compture but its another option.