Becoming sexually aroused by people from Great Britain. This can either be a heterosexual attraction (if your natural attraction is for members of the opposite sex from Great Britain) OR a homosexual attraction (if your attraction is to members of the same sex from Great Britain). This fetish seems to be most common amongst the citizenry of the United States of America.
For Americans who cannot hear the difference between an accent from the three countries of Great Britain (England, Scotland and Wales) and the accent of someone from IRELAND - often times a Brit Fetish and an Irish Fetish can be confusing and/or synonymous.
"Oooooh - Colin Firth, Daniel Craig, Clive Owen ... they are SO hot! I think I have a Brit Fetish ..."
"Really? It's Colin Ferrell and Liam Neeson who do it for me!"
"Silly Yank! You don't have a BRIT Fetish! You have an IRISH fetish!"