Probably the most popular example of adult cartoons is Family Guy. The same kind of people who were quoting Bart Simpson fifteen years ago (Don't have a cow, man!) are quoting Stewie Griffin today (Damn you, vile woman!). But while The Simpsons do, in general, try to end on a moral high-note, Family Guy has no such hang-ups.
Remember when they beat the crap out of each other? Good times.
Take the Simpsons and invert the kids (Chris is stupid where Lisa is smart, Meg is a push-over where Bart is brazen, Stewie is maliciously evil where Maggie is, well, a baby), add random pop-culture tangents, amp up the violence and sex and you've got the Griffins. My parents wouldn't let me watch The Simpsons when it first came on the air. I'm pretty sure they wouldn't approve of me watching Family Guy now, and I'm twenty-five.
Stewie says, "I may kill you tonight."
It's not the inappropriateness of Family Guy that makes me love it so, but that fact that it is perfectly appropriate for my age group. I'm young enough to enjoy bathroom humor but old enough to get Dick Van Dyke references, and Family Guy has both. And I'm not alone - this show was canceled and brought back not once but twice. It doesn't have so much a 'cult' following as an 'almost everybody you know' following. Plus, it's been banned in Indonesia, Taiwan, Vietnam, Iran, South Korea, South Africa, and Malaysia.
So don't turn your nose up at Family Guy, either because its too childish or too adult. You don't know what you're missing.
A family after my own heart.