If memory serves me....
Two pieces of Sh!t come to mind. However, they didn’t have to fall into that classification but due to the US Government (Navy and Army) they eventually fell into the Sh!t category.
The first was the Sikorsky S-52 (HO5-S) which was by design a very good helicopter. The US Navy kept adding electronics systems, which made the helicopter, underpowered. Sikorsky wanted to upgrade the powerplant but the Navy refused saying that they had a surplus of engines, which were used in Bell helicopters. When the S-52 finally entered service it was vastly underpowered, it could not carry the full compliment of passengers and with a pilot and Co-pilot it could not sustain flight with one magneto inoperative. The Marines and the Coast Guard pulled them from service and placed them in long term storage.
The second was the Cheyenne. Because the US Army kept adding weight to the helicopter Lockheed requested that they be able to increase the rotor diameter to compensate for the increased weight. The Army refused the change so Lockheed designed the blades to improve their lift characteristics. The blade design was a far cry from standard blade design in that the blades had an unsymmetrical airfoil and that the shape of the airfoil changed at different blade stations. This caused the blades to become unstable with unpredictable phase angles resulting in the loss of two helicopters. It took several years to design a system that would compensate for the changes in phase angle but by that time the Army cancelled the program.