HSDD = Heavy Sigh of Deep Depression (followed by an actual heavy sigh)
In the late 1970's and 1980's High School and College during studying for tests, finals or in class when a teacher announced a pop quiz (we were rarely prepared for) we'd look at one another and say HDDD.
IBM was not only a large national corporation but it moved the employees around frequently, so as kids we grew up with parents using Three Letter Acronyms (TLAs.) As kids moved in and out of our schools all around the country and world, we started the term so the adults would not know what we meant, and it lives yet today among many generations.
Then: "Oh no, not a quiz, HSDD."
Now: "The President just tweeted again, HSDD"