if this is truly your friend, cut them some slack. no one expected all this growth in such a short time. and to call in that marker at its peek valuation is kind of rude, if this is your bro (im assuming you know his situation, there is a reason why he hasnt paid you back yet. this is one of the few types of debt that may grow over time, and a new thing to the financial sphere. at the best, charge him the usd price from the time when he borrowed the coins. at the worst, get SOME of the profit you would have had if you had kept your coins, but understand while he may owe you money, he has a legitimate reason to be salty about this. his loan went up over 100% .

how would you feel about your mortgage if you had to pay half as much again, suddenly?