What does the term 'vacuous' imply about a person's demeanor?

The term 'vacuous' is commonly used to describe a person's demeanor as lacking in intelligence or thoughtfulness. It implies a sense of emptiness or superficiality, often suggesting that the person exhibits a foolish or naïve attitude without any substantial insight or depth. In the context of the provided choices, the option indicating "complacently or inanely foolish" aligns perfectly with this definition, as it emphasizes a lack of seriousness or thought that characterizes a vacuous demeanor. The other options suggest traits such as wisdom, confidence, or emotional balance, which are contrary to the implication of vacuity. Therefore, the correct answer reflects an understanding of vacuousness as an absence of intellectual depth or meaningful content in a person's behavior or statements.