I try not to use nicknames unless a person has used it themselves, which can be difficult as navigating your way through an array of people with the same name can be quiet the challenge. My experience has mostly being that people are highly offended, but interestingly most seem to concede to theirs by mid life, unlike 1of-dem very few are willing to embrace one so readily.
I've also noticed that using the nickname of someone who has passed is very murky water as unless you are related by direct kin that rarely gets a good reaction.
Gamybure I totally agree with you, it is very Irish and undoubtedly whispers on through our Celtic heritage.
In a way most of us have a trinity of names.
Our family name, clan like and marks the lineage from which we were born.
Our first name, often inherited and passed on through significant loved ones and
Our own unique moniker, which marks both a belonging and placement within the community.