Mothers Against Canada was an anti-Canadian organization formed by Sheila Broflovski in South Park: Bigger, Longer & Uncut. Mothers Against Canada is likely a spoof of organizations like Mothers Against Drunk Driving and other more offensive Mothers Against-related organizations.
After seeing the Terrance and Phillip movie "Asses of Fire", and getting into an argument with Eric Cartman about the plausibility of setting a fart on fire, Kenny McCormick died to just that. Blaming Terrance and Phillip for the death of Kenny, Sheila Broflovski started an organization to raise awareness of the "evils" of the Canadian people. After a public rally, and a big musical number, Mothers Against Canada (M.A.C.) was formed. Eventually, M.A.C. gained enough influence to persuade the President of the United States to declare war on the Canadians.
In their protests, they demonized the Canadian people, solely blaming them for the profanity that their kids were using and the obscene acts they had been persuaded into doing. Sheila went so far as to advocate senseless violence against them as long as there was a total lack of foul language. Through all of this, they deliberately ignored the fact that American entertainment was just as guilty of encouraging foul acts such as swearing, if not more so.
M.A.C. eventually secured the arrest of Terrance and Phillip while they were on the Late Night Show with Conan O'Brien, and was charged with executing them before the U.S. Army in South Park before they were sent out to destroy Canada. Although the duo were saved from their execution thanks to the show's main characters, Sheila later shot them both dead, thus spawning Satan, his partner and lover Saddam Hussein, and the entire army of hell, as part of a prophecy that called for the culmination of these events. It was this act of violence that nearly led to the destruction of the world and an era of permanent darkness that was only stopped by the show's four main characters.
Ironically, the very thing M.A.C. tried so hard to abolish was what saved them from Satan's wrath. Cartman's V-chip, which was designed to shock him when he swore, malfunctioned during the chaos and gave him the power to electrocute his enemies, greatly enhanced by his profanity. Cartman easily defeated Saddam through his intense swearing, saving the world.
- "M.A.C." is ironic, since a common stereotype with Canadians is that they eat Mac & Cheese more than anywhere else in the world.