When Cartman has Asperger's Syndrome, he has his own way of dealing with the disorder. By calling it "Ass Burgers" and planting burgers in his butt of course.
Added:

South Park Season 15 Episode 8 Quotes

Nurse: Why are there hamburgers in your underwear?
Cartman: Are you serious? You're saying I have Aspergers?

That's just your brain levels adjusting back to the real world.

Cynic