Which of the following is an example of an 'eccentric' behavior?

Eccentric behavior is characterized by actions that deviate from the norm or expected standards, often in a quirky or unusual way. Wearing a tuxedo to a casual gathering exemplifies this concept because it involves dressing in a manner that is significantly more formal than the surrounding context would typically warrant. This choice disrupts the usual expectations for attire in a casual setting and highlights uniqueness or nonconformity, which are hallmarks of eccentricity.

The other options, in contrast, reflect behaviors that align more closely with societal norms or common practices. Following a strict dress code is indicative of conformity, as is choosing a common hobby or reading widely accepted books. These actions do not involve the same degree of deviation from what is typically expected in social situations, which is why they do not illustrate eccentric behavior in the same way that the first choice does.