What word or phrase does your mother always say?
/dow/ [German Fidonet] D"ummster Anzunehmender User. A German acronym for stupidest imaginable user. From the engineering-slang GAU for Gr"osster Anzunehmender Unfall (worst foreseeable accident), especially of a LNG tank farm plant or something with similarly disastrous consequences. In popular German, GAU is used only to refer to worst-case nuclear accidents such as a core meltdown.
See cretin, loser and weasel.