When I moved here I joined a few meetup groups, with the obvious goal of meeting people and getting out to experience life in Ireland. At one of the meetings, a coffee shop, where I answered the usual questions around why I moved, where I'm from, my opinion on the weather, etc. I heard an American accent. It was a rarity because at the time I had encountered few US citizens living over here. The girl using the accent however responded with, "I just get here and one of the first people I talk to is an American, " offended at having to talk to another American. I found it to be a bit rude, and went back to the conversation I was having prior.
Recently I was out on one of the Irish evenings involving beer and social interactions, and during this event was introduced to another US citizen. We shook hands, where he did the typical American thing of trying to grip as hard as possible and be an annoying douche. Luckily the conversation didn't last beyond the introductions. He went back to hitting on the girl he was talking to, and I went back to talking to someone interesting. Meeting this guy and a few others I've met actually make it clear why Americans have the reputation we do, of being overbearing douche-bags.
As time has gone on, I occasionally encounter other ex-pats living in Ireland and with few exceptions I find them annoying to be around. I mentioned this to someone else, who said the same thing. Not just Americans but about people from their own country. She said it had to do with meeting people other than her countrymen, and I could see the rational about that. As one of the few Americans in my social groups, there is a uniqueness about being the only one. So when I suddenly lose that uniqueness it makes me dislike the person who caused the loss of my uniqueness.
It is more than that however, because I've met other ex-pats who are perfectly good people to be around. I work with a guy who moved here from the US office, and he's a good guy. One of my meetup groups has an ex-pat in it who is also a good guy to talk to. But when it comes down to who I spend my time with, not a single US citizen in the bunch. Just like the French live up to the reputation of being arrogant and rude, Americans tend to live up to the reputation of being overbearing jackasses and so I tend to avoid them.