2x1 - South Park

The show starts off with the build up from last season's cliffhanger revolving around Cartman's paternal origins. However, just as it seems they are about to get on with the second half of "Cartman's Mom Is A Dirty Slut," they do a 180 degree turn-around and reveal that for April Fool's Day they will be showing Terrance & Phillip in "Not Without My Anus".