First, put an ad in Craigslist and find a hacker that can break into the client's CMO's computer and find whatever kiddie porn sites he's visited. If he hasn't visited any, have the hacker make it appear as if he has.
Second, send the client a dead fish wrapped in last week's edition of Ad Age magazine with the message: "Put your account up for review and your family is going to have to come down to the pier to identify your body."
Third, have your designer photoshop a picture of the client in Michael Jackson's bed at the Neverland ranch. Have him put in the CareerBuilder's monkeys for good measure.
[Note: Best to have the designer killed off when he's completed the job so the trail doesn't lead to you so don't use your best person.]
Forth, tell the client "You can't fire us because we're dropping you." One in five times, a really insecure client will keep you as their agency if you confuse them with this one.