A useful word: MUMPSIMUS.
Wikipedia provides a good definition: “A mumpsimus is an action by a person who adheres to a routine, idea, custom, set of beliefs, or a certain use of language that has been shown to be unreasonable or incorrect. For example, a person may continue to say all intents and purposes as all intensive purposes, even after being corrected. The term mumpsimus may also refer to the person who performs the action.”