There was a whole episode about a boy with an arse for a face, and when he spoke it sounded like farting. IIRC, Kenny posed for the school photo with his hoody on backwards so you saw his arse; then Cartman sent that picture off to the milk carton people who advertise for missing people. Then a couple claim that the picture is their son.
As for the rest of the show, I have no problem with it being "hit-and-miss"...if you watch back the old Two Ronnies shows, there is an awful lot of hit and miss on that, but maybe that just my age.
Numberwang is definitely my favourite part of that show!