den Teufel an die Wand malen — To paint the devil on the wall. Duden: to bring about a misfortune by talking about it. It comes from a practice used when calling up the devil.
die Unke and unken — The Unke is a fire-bellied toad. In everyday speech it is also a person who keeps predicting bad things. Duden gives the example er ist eine alte Unke, he is an old toad.
der Schwarzmaler, die Schwarzmalerei — The black-painter and black-painting. Duden lists Pessimist and Unke as synonyms, and gives Endzeitstimmung and Weltuntergangsstimmung, an end-of-the-world mood, among the synonyms for the habit.
These words mock habitual gloom. None of them is aimed at a single, specific objection.