Which Animated Series Must Never Get A Live-Action Movie?

Tons of classic animated series have become live-action films, including the Smurfs, Garfield, Avatar: The Last Airbender, and the Teenage Mutant Ninja Turtles. And often... it doesn't work out that great. But which animated series or cartoon must never, ever become a live-action movie? Ever?

Please include a picture or clip (or comics panel) for your chosen cartoon or animated series that must never become live-action. And please mention the name, and why it's so unsuited to the live-action format. Thanks!

Top image: The live-action version of Adventure Time that was created as a ridiculously cute promo on Cartoon Network. But we still don't want an actual live-action Adventure Time. Nope.