Based on your logic, zazarb should be entitled to ask you for more in re-payment whenever the price of BTC drops following the initial loan. After all, he lent you a certain value in USD and is getting a lower value in USD returned to him. It doesn't look like you were complaining when that was the case though. If you wanted a loan denominated in USD or another fiat currency, you should have added that to the terms. You knew Bitcoin was volatile, yet deliberately avoided repayment in the hope that the price would drop. It is now almost an entire year after you first entered into this agreement and you still haven't even repaid the principle. Zazarb has been more than lenient by waiting until now to publicly call you out on this. I will remove my feedback once this issue has been resolved to the lender's satisfaction.