There is a very common theme in Family Guy; namely, that Meg is insignificant. This is a very sick joke when you piece together the little bits of the message. Very often, Stewie makes a little remark here or there, suggesting that Meg’s unpopularity is based on her ugliness and that she could do something about it. Some other characters (James Woods) also are constantly recommending that she engage in bulimia and/or anorexia nervosa, said in a way that is a helpful suggestion to get friends and improve her life.
Perhaps the darkest aspect of the theme is that it isn’t an explicit ‘joke’ in the same way as the digression gags are obvious jokes. These are minor comments about a majorly upsetting suggestion. That is a very subtle and very successful way to put forward a powerful derisory comment. It’s quite powerful, its quite amoral, and it is pushing very much the limits of sensibility in terms of a joke. I don’t think its a very good joke, either, but then again, it’s not supposed to be, as Meg is typically a minor character.
I do remember once watching Family Guy with an Evangelical Christian friend of mine, and we both laughed, even though guiltily. I find the phenomena of immoral humour to be psychologically interesting; similar to the question of how we may find beauty in evil.