Contrary to the comment about Karen sticking her pinky in the jam, then tasting her ring finger, - she actually does stick her ring finger in the jam, not her pinky.
The running joke of the episode is that saying "F and E" sound like a half censored swear word.
When Mayor Fitzy askd Karen to taste the jam he just put on her desk; she dips her pinky finger in the jam, then tastesher ring finger.