Space Quest/Nightmare Fuel

Space Quest I

 * Make Roger fall into Acid or Lava and get ready to change your pants.

Space Quest IV

 * Right at the beginning of the game, you have a chance of encountering a ragged cyborg wandering the streets. Should you get too close, you're treated to a Gross Up Close-Up of the poor guy's face before he lets out a blood-curdling shriek that alerts the nearby Droid-O-Death, which then shoots you. The whole sequence scarred more than a few kids back in the day.
 * Also the slime in the sewers, which would suck up Roger only for him to briefly come out half-dissolved with part of his skin melted off.