Mod support in PC games is common for adding things like user interface tweaks or weapons and armor. In a game like Civilization 5, which is all about the methodical building of society itself, mods can get a little wild. Like putting your nation-state in the hands of two cartoon idiots, for example.
The Beavis & Butthead mod on the Steam Workshop (via Kotaku) seems well thought-out, at least in terms of the perks and drawbacks you should expect from selecting them to run your country. Since "Thinking Sucks," your Great Person production, Wonders production, and influence degrade much faster than usual. On the bright side, your citizens will be less unhappy in response to overpopulation, because they are dumb.
The pair also get a few of their own unique builds. The Hot Chick Museum replaces regular museums, and Burger World replaces the hospitals. Finally, the mod features a unique "Cornholio Project" national wonder, which produces (obviously) one super-powerful Cornholio unit.