Ewww, That's Growth

The episode "Ewww, That's Growth" is about Dexter being upset about his pint-sized height; one of the ways his stature makes his life harder is that he's denied going on a rollercoaster with his family. After he makes himself very tall with an invention of his, he is allowed onto the ride and proclaims that this is the greatest day of his entire life, only for his head to hit the tunnel followed by a quick cut to black that ends the episode. The implication is either that Dexter died, or more realistically, got stunned from hitting the tunnel (which would have required medical attention in a more realistic work with such setting).

Example of:
Downer Ending