Topic of the Day: I don't think I've seen a truly "bad" professional production. A lot of bad community theater productions (I ushered for most of them so I didn't pay to see them), but not a bad production by a real professional troup.
The absolute worst community theater production that I saw was (appropriate for today)
Little Shop of Horrors. It was put on by a group that no longer exists called Puget Sound Theatre Ensemble (affectionately called "PEST"

). It was a truly horrid production. The Audrey couldn't stay in tune and all that they did for "Close for Renovation" was add one little vase with a single flower. That's it. That was their entire "renovation!" The voice of Audrey II was a local political "celebrity" who was not only not good, but just totally wrong. But he fit in with the rest of the production.

The actors playing Seymour and Orin were both pretty good. And the three urching weren't bad. A couple of years later, I did a show with one of them and she told me that the so-called choreographer didn't do anything with them! They had to make up all of their own dances and movement!
The performed it on the main stage of the Washington Center for the Performing Arts (where I usher frequently), a house that seats 988 people. This is not a show that can play in a theater that big. Anyway, they had a special Halloween night performance and if people came in costume, they could get a discount on the ticket price. Only 30 people showed up...total! Not 30 people in costume, but only 30 people in the whole theater!! Fortunately (especially for the young actors in their "training courses"), they eventually folded and are no more.