For some definition of dark comedy/humor: http://en.wikipedia.org/wiki/Black_comedy
That being said, while the Simpsons sometimes show us 'feel-good' moments and other heartwarming aspects, sometimes the show shows dark aspects that reminds us that the world is not really much of a fairy tale with unicorns shooting flowers out of their horn. That being said, I love dark comedy at times because it can be spooky, scary, ironic or sometimes even give us something to think about for the indirect attempt at more humor. It's not really realistic mostly, but I think it does a good job on making audience laugh for the purpose of humor.
One thing that I can think about is Sharry Bobbins getting sucked into the airplane engine in the end of "Simpsoncalifragilisticexpialad'ohcious'. It was random, somewhat shocking, and yet ironic to what the family was saying after her departure... I ended up laughing hard, with somewhat of guilt.