Anything I've ever written that's originally supposed to be a quick prototype and ends up staying around a while. My problem domain requires a lot of throwaway prototyping by its nature. For these prototypes, it's sometimes reasonable to violate every best practice and rule of good style, just get it done and clean up later if the prototype ends up being worth keeping. However, occasionally these prototypes end up being very difficult to get working properly, but then end up being keepers. In these cases, I usually end up putting off refactoring/rewriting the thing indefinitely because I'm afraid I'll never get it working again. Further lessening my motivation is that my boss is a domain expert who doesn't program at all.
