I remember the days of SNES and Genesis ad wars, Sega trying to make Nintendo look bad. It was hilarious, and that time was made famous for shitty ad's that were somehow awesome. Kids used to argue about how the graphics on SNES sucked and Genesis was better because it had games with blood in it (Mortal Kombat). Ahhh I used to love those heated (yea I know) arguments in the lunchroom. People getting royally pissed because someone said that Genesis looked like a bad space movie prop. Check this ad below form a list I found at 1up.com.
There are more at 1Up, Best Worst Game Ads.