I must confess I've done the 'plastic paddy' thing myself just because it can be good fun... I'm sorry--is this color making your eyes bleed? Will switch to...

I can find loads of things that are worth the aggravation of getting insulted by. This is not one. It's just, appropriately, about those who are Irish only when it suits them. It's just like people who get all churchy and halleluliafied on holidays but don't give religion or their church another thought the rest of the year. I play some Irish music, but I've been known to wear a leprechaun hat and go silly with green at times BECAUSE IT'S FUN. I can 'pass' for Irish, but I don't actually call myself Irish. I don't call myself English either, though that's where about 80-90% of my ancestors came from. Folks in the UK might call it 'race', but for me, it's culture.

The term can be used to dismiss people who are hyphenated Irish, but is usually done because the person using the term has no clue about the target's background. You can view this sort of usage as an insult (it's meant as one) but ultimately it's a big old 'Hi. I'm an idiot and don't have an argument so I'm trying to belittle the other person. Now that you know I'm a complete f***wit, KICK ME!' sign.

So yeah, it can be an insult, but it says more about the person saying it than the person so labeled. To know whether a person is adopting a persona to associate temporarily with some group temporarily or IS that person, you have to know him.