A public plaza that has degenerated into a giant traffic funnel.
Place de la Concorde is the worst of all public spaces in Paris because it exists solely to move traffic. This square, the biggest in Paris, is 21 acres large. Calling it the Place de la Concorde ("Square of Peace") is the height of irony. Its history of slaughter, (over 1100 people were beheaded there and another 133 trampled to death), is recalled by the racing traffic that constantly threatens to run over the substantial flow of pedestrians traveling between the Tuileries and the Champs Elys_es. Hopes of walking comfortably from the Louvre, through the Tuileries, to the Champs Elys_es are immediately dashed upon encountering this asphalt wasteland. Nowhere can you find so vast an expanse of vehicle-dominated space that is less necessary than Place de la Concorde. The vehicular space could be reduced by 80% and there would still be a smooth flow of traffic. Instead of an enormous void, this could be the central point in all of Paris -- a historic destination, a gateway/transition space, and a great event center. From its vantage point there are fabulous vistas of many noteworthy monuments. More than any other single space in Paris, Place de la Concorde could be transformed from a spectacular failure into a sublime, transcendent urban space.
*Please note that these Hall of Shame nominations were written in a moment in time (most over a decade ago) and likely have since changed or even been transformed. If the above entry is now great, or still not so great, go ahead and comment below on how it has evolved or nominate it as a great place.