Former FTX exchange CEO Sam Bankman-Fried, now in New York's Metropolitan Detention Center, reportedly used mackerel as currency to pay for a haircut. Mackerel, known as "macks," has become the prevalent currency in federal prisons since the 2004 cigarette ban. This shift highlights a reliance on tangible commodities in environments where traditional currencies are inaccessible. The price of mackerel has risen by 30% to $1.30 in prison commissaries, reflecting inflation and demand. The use of macks as currency is humorously compared to the stability of the Mack currency system versus the volatile crypto markets by a former inmate and prison consultant.