Prior to 1982, it was considered taboo for a company to mention one of its direct competitors in its advertising. (In a lot of countries it is outright illegal, even today.) It just wasn't done. Along came Burger King and their advertising agency J. Walter Thompson. BK and JWT decided to create an ad taking on the behemoth of burgers: McDonald's. They aired an ad on television featuring a cute little 4 year-old actress who proclaimed, "I only eat at Burger King". They also made claims that their burgers were 20% larger than McDonald's, among other things. Those of you who have ever met a lawyer or who know anything about McDonald's know that this is where the meat hit the grinder, so to speak.
McDonald's at this time still had their sesame seed buns in a wad over the pernicious but false rumors that their burgers contained worm meat and their milkshakes had cow eyeballs in them. (If you don't know what I'm talking about, ask your parents.) There was also the ugly business involving the Hamburglar, who is now known as the Hamregisteredsexoffender, and the fact that their coffee stirrers were being used as coke spoons (that one is true, but don't ask your parents because they'll just deny it). Mickie D's, being a multi-billion dollar corporation, had a couple of lawyers with nothing better to do (which is when a lawyer is the most dangerous) than sue the crown off of the Burger King.
McDonald's didn't just go after the ad agency for defamation, they also sued the 4 year-old actress who starred in the commercial for false advertising. After intense cross-examination by one of McDonald's
The actress in that commercial was none other than Sarah Michelle Gellar, star of Buffy the Vampire Slayer, The Grudge, Cruel Intentions, I Know What You Did Last Summer and It Wasn't Very Nice, etc.
Sarah Michelle Gellar got her big break as the star of the TV version of Buffy the Vampire Slayer. One of the primary sponsors of that show? McDonald's...the same company that had sued her when she was 4.