Any party that's suing a bank will act the part of the unsophisticated victim, even if they knew exactly what they were getting into.
If a salesman offers you a bet that Citi shares will go up, and you take the bet, and Citi shares go up, and you don't get any money, and you ask him what happened, and he shrugs and says "derivatives are complicated, man" -- you should probably sue him. But if a salesman offers you a bet that Citi shares will go up, and you take the bet, and Citi shares lose 96 percent of their value, it looks a little funny to go to court and say "well we didn't understand the structural nuances of the bet." The nuances are not your problem.