Where's Herb? was their disaster of a commercial Burger King aired in the 1985-86 season.
The spots revolved around the character of "Herb", a person who claimed he had never eaten a Burger King burger in his life. Burger King used this to attract customers in hopes of finding this Herb. In addition, customers could get a discounted Whopper by including the phrase "I'm not Herb." in their order. But, however, Burger King blundered, because they revealed Herb's appearance during Super Bowl 20 in January 1986. Once his appearance was discovered, people began to lose interest in Burger King, and the company lost 40% within three months, no lie.Remember, this is a totally true commercial, read the Wikipedia article.
It's right below me.