What are the parameters for "لباس الشهرة" (garments of fame/vanity), and do modern Western clothes fall under this category, or is it restricted to what is worn by decadent Western celebrities or European monarchs in the Middle Ages?

The criterion for garments of fame is that they go against what people are accustomed to in clothing, whether in color, description, style, height, or lowness. A garment of fame does not have a specific form; rather, it is whatever makes a person famous or pointed out because of it, and it is outside the common customs of people, so that it does not become a reason for backbiting a person.

From the above, it is known that some modern Western clothes are considered garments of fame, and some are not. This depends on the custom of the country where these clothes are worn.

As for clothes that are exclusive to disbelievers, it is not permissible to wear them. The attire known as trousers and a shirt is not exclusive to disbelievers; rather, it is a common attire among Muslims and disbelievers in many countries.