It is the fungal stain that appears where there is moisture, but associating with the phrase "boring as a fungus" is said of someone who is annoyed; that in subsequent meanings already names who has or attracts bad luck, who is fucked. By extension, the same bad luck or misfortune. It comes from the Veneto star muffo ("to be sad") that takes it from Latin mucere ( "hongo" ). See yeta .
