Michael Wex has this to say about the phrase "Kadokhes mit koshere fodem"
Kadokhes is a fever, especially a recurrent, malarial fever, the kind that always comes back just when you think you're done with it. It's used in curses and as a nastier stand-in for bupkes. Kadokhes vel ikh dir gebn, “Fever is what I’ll give you,” means that you get nothing but my contempt.
Adding kosher thread to kadokhes takes things into the realm of “Sweet Fanny Adams.” In times of distress, especially in cases of serious illness, women used to go to the cemetery and lay thread around the grave of a notably pious person, as if they were taking its measurements. The thread—known as koshere fodem--was used to make wicks for candles that were then donated to the synagogue in an effort to arouse the mercy of heaven. Making such candles was called leygn kneytlekh, “laying wicks,” and was an organized group activity, a kind of bee, a cross between a tea party and a women’s prayer meeting.
In kadokhes mit koshere fodem, the heartwarming piety that would normally have suffused a phrase like koshere fodem turns into its opposite. The idea is: “All you're going to get from me is a fever so bad that they'll be measuring graves and making candles in a desperate attempt to save your life.” The koshere fodem is similar to the English “. . .and the horse you rode in on”—it makes the curse even worse.