The dirtiest hotel is Grand Resort Hotel Pigeon Forge, Tennessee.
Here is the link for the US hotels.
This is horrible... I have seen some pretty raunchy hotels in my time, especially in Miami and on our road trip to Myrtle Beach, but never quite that bad or gross.
TripAdvisor does this list every year and they also have the lists for Europe, Asia, and India.
Europe's #1 dirtiest hotel is...Club Aqua Gumbet, in Gumbet, Turkey.
Most of the hotels were in London and Amsterdam so be careful where you stay!