Leaving aside your rather ill-informed history lesson - indicates to whom?
As a British born non-catholic who has lived and worked in both Ireland and the UK, I can assure you are over-stating its meaning, except perhaps to practicing loyalists in Northern Ireland. The accepted vernacular there as a matter of practical sensitivity to the majority is "Southern Ireland" or "The South" and "GB" for the part of the UK that excludes NI.
To suggest that it is generally offensive (as in "giving the finger") is, well, offensive.
As a British born non-catholic who has lived and worked in both Ireland and the UK, I can assure you are over-stating its meaning, except perhaps to practicing loyalists in Northern Ireland. The accepted vernacular there as a matter of practical sensitivity to the majority is "Southern Ireland" or "The South" and "GB" for the part of the UK that excludes NI.
To suggest that it is generally offensive (as in "giving the finger") is, well, offensive.
Edit: To wit - "UK Border Agency | If you are travelling to or from the Republic of Ireland [...]" http://www.ukba.homeoffice.gov.uk/customs-travel/Enteringthe...