Mentos. Breath mints do not give you the power of having your wishes come true. Blatantly idiotic, yet the ads ran for years. For all I know they're still on (I don't have TV).
Axe body wash/spray/sniffle/what-the-F-ever, for the same reasons. If you look like the guys in those commercials you do not need to use product, women will like you. If you don't look like those guys, no amount of product can save you.
The Big Kahuna. That movie where Kevin Spacey and Danny DeVito are businessmen? Advertised as a bucket of laughs. Really a dark comedrama. Not a bad movie, just utterly misrepresented.
Sideways, the movie where Paul Giamatti and Thomas Haden-Church take off for a week of fun up the coast. Advertised as a "critically acclaimed romantic comedy." Want to know how romantic it is? Giamatti's character is at an all-time wine-soaked misanthropic low over a failed relationship and couldn't enjoy himself with a woman to save his life. Haden-Church's guy is getting married the day after they get back, so his goal for the week is to cheat on his fiancee as many times as possible. I don't know about you but adultery and drunken self-pity are certainly the ways *I* spell romance. As for comedy? Same deal. My mouth didn't twitch once. I don't know what critic signed off on this stinker but it's one of the few things I've ever seen where I wanted my 90 minutes back. The one thing I can say in its favor is it doesn't involve any of the usual rom-com formula bullshit.
I was very angry seeing the PlayStation marketed to jocks and knuckleheads. I'm plagiarizing somebody here -- Tycho, maybe? I can't remember -- but games belonged to the outcasts. The popular good-looking soccer player types already had friends, and sports, and girls. Why did they need games? It was a great blow to nerd exclusivity.