Not in military or political terms - though that happens too - but for simpler things. America is the enemy of the fight against obesity, against consumerism, the fight to save the planet. Even, sometimes, of common decency, a modicum of modesty, and good old-fashioned politeness.
Hollywood is to blame for a lot of it. Even though Hollywood itself is probably one of the most densely populated centers of people who are obsessively thin, fit, green, and left-leaning, the America it manages to portray to the rest of the world is skewed. We see the extremes, rarely the norms. Because the extremes are more interesting and more fun: they tell better, funnier, sadder, more money-spinning stories. (Because Hollywood is about consumerism. They can't get out of that one.)
But I'm here to tell you that it's a shame. Americans are the politest people I've met. They work harder than anyone else, and whatever they rush to the shops in their enormous cars to buy in bulk, they've damn well earned. (For the most part.) Far from being the sex-crazed heathens so often seen on screens, a lot of middle-Americans are as just repressed and guilt-ridden as their Irish counterparts, if not moreso. Jewish guilt and Catholic guilt cover much of the same ground.
Americans are nice people. They come from a country so vast and variegated that sometimes it's hard for them to see - by which I mean, travel - beyond its borders. Those of us from smaller countries, who can easily travel abroad to places where people speak other languages and live in different ways, eating different things for breakfast and dressing more stylishly, find it easy to scorn someone who has never left their native country; but if you lived somewhere with so many amazing things on your doorstep, you might not either. Many Irish people are more familiar with Benidorm or the Algarve than with the Ring of Kerry or the Giant's Causeway, and that shouldn't really be a point of pride.
Americans are proud of their country, and they show it in ways that some others may find a bit in-your-face, with all the rampant flag-waving and God-Bless-America-ing - but the sentiment is just the same as that of all the Irish people who get obnoxiously drunk and paint their faces green white and orange when our team gets past the first matches of the World Cup. (Any sport.)
So if you're in Dublin and you see some Americans on the Dart, announcing their origins with every step of their bright white runners with their stone-washed, high-waisted, tapered-leg jeans, looking for their roots and being delighted anew at all the quaint, be nice to them. They'd be nice to you.