I’ve googled this, but looking for precedents to not use the correct, formal answer.
We’re having an event today (in about two hours) where the Archbishop is coming to dedicate a building. Prayers, sprinkle holy water, read the gospel-- the whole shebang. It will be a very informal outdoor event. There will be about 100 people attending, many of them greeting him, shaking hands, getting their picture taken, etc.
Googled answers say to address him as Your Grace or Your Excellency… which I’m sure is the strictly correct, formal answer. Would it be okay to call him “Father”? Would that be a huge social gaffe resulting in being condemned to the fires of etiquette hell (even for us non-Catholics who don’t believe in hell)?