Final answer:
The correct vocabulary word to complete the quote is 'etiquette'. Etiquette refers to the customary code of polite behavior in society.
Step-by-step explanation:
The correct vocabulary word to complete the quote from 'To Kill a Mockingbird' is etiquette. The sentence uses 'her use of bathroom etiquette leaves nothing to the imagination.' Etiquette refers to the customary code of polite behavior in society. In this context, it suggests that the person's behavior in the bathroom lacks proper manners or decorum.