Not sure you can avoid negative or neutral feedback but you can sure avoid losing your money and wasting further time on this unreasonable buyer.

My advice would be to refund this customer and close off the dispute.   If at all possible to lodge an unpaid item dispute after the Paypal dispute closes off - I would do so.

In order to win the dispute you would need to show paypal an approved method of trackable postage (such as registered post or click and send).   Therefore if you hadn't planned on sending the dvd using a trackable service then refunding this buyer is the easiest and best option for you at this point.

Sadly these kinds of buyers are multiplying on eBay.  Sorry that you copped one of them ekrabappel.  All the best for your upcoming trip!