too many chefs in the kitchen
Too many people are trying to control, influence, or work on something, with the quality of the final product suffering as a result. (A variation of the more common phrase, "Too many chefs spoil the broth/stew/soup.") A: "The more that goes wrong with this project, the more people get involved. Now we've got my boss, his boss, the assistant manager, a freelance consultant, and the head of IT all involved, and it's turning into a complete disaster!" B: "It sounds to me like there are too many chefs in the kitchen."
chef d'oeuvre
A masterpiece. When the sculpture was finally complete, the artist declared it his greatest chef d'oeuvre.