This wasn't a week to remember for Korea-based e-commerce specialist Coupang's (CPNG 0.20%) shareholders. According to data compiled by S&P Global Market Intelligence, from last Friday's close to this one, the stock declined by almost 11%. But that wasn't surprising, considering that a researcher from a top U.S. bank downgraded his recommendation on the shares.Citigroup downgrades Coupang to neutral from buySpecifically, this was Citigroup's John Yu, who on Tuesday before the market open changed his rating ...