Any given place where more than one badass can reliably be found. In modern times, this may mean a certain night club, a certain seedy bar, or even any given trailer park - depending on the inhabitants.
Historically, this was named after the Badasserarium in Brundisium, a temple erected by Emperor Nero in the year 55. The original Badasserarium honored the final, most badass professional fighters left standing after the Great Gladiatorial Gangbang in July of that year. The survivors of a massive day-long free-for-all initiated with 900 heavily armed and alcoholically lubricated gladiators, these handful were granted the honorific Badassissimus, indicating status of an ass far worse than any other precursors in the field of badassery. Enshrined during their lifetimes as living saints of the Badasserarium, such was their fame that even respectable matrons and virgin girls of Brundisium would pay good money to spend fifteen seconds with any one of them, who would bestow his virility and virtue upon them with a Falcon Punch to the abdomen, leaving them unable to walk - sometimes permanently.
Upon being asked by Nero whether this was absolutely necessary, the Badassissimus responded by roaring incoherently and kicking a watermelon hard enough to orbit the known world twice and decapitate a nearby catamite the following Thursday. Suetonius translates this to mean: "Yes, I am afraid it is."
"This San Francisco restaurant once served lunch to Bruce Lee, Kareem Abdul-Jabbar, and Chuck Norris at the same sitting. For the brief duration of that lunch, decades ago, this restaurant was a badasserarium."
"The Badassissimus of the Badasserarium was a badass well known for his consummate badassery."