No, it's not a question of how much Guinness you drink, or whether you'd die first before donning an orange sash. It's who your nearest Irish relative is.

The exchange goes something like this:

"So you're Irish"

"Kinda, yes," I reply while thinking, "Oh dear, not again"

"So your <insert ancient relative here> is from Ireland?"

"No, my mother left at about my age"

"Ah, well that's ok then."

As near as I can guess, this game works something like this: If you were born here, but dragged off to America by the 'rents, you're at the top of the heap. One or two parents from here, but born in the states: you might be acceptable. After that, you're pretty much out of luck. Dunno how your luck runs if you're from somewhere other then the states. I'm guessing you get a touch more slack.

Don't get me wrong, no one is mean about it or anything, people just like to protect their groups. Wouldn't want a bunch of bloody foreigners pissing on the shamrock, so to speak.