Donnybrook is a district of Dublin, Ireland. It used to be the site of Donnybrook Fair. It began in 1204 when King John bestowed the eight-day event on the citizens to thank them for fortifying the city of Dublin. The fair became notorious for drunkenness and rowdiness giving rise to the word donnybrook. The fair was eventually banned in 1855, but the word stuck.
Usage example: .....the donnybrook on Capitol Hill over immigration.....
Sources: answers.com, http://www.donnybrooktennisclub.ie/content/info/history.jsp