Only if you talk strange like an Aussie! We just can’t mush words together like you guys can.
Irish: Paddies
Scottish: Jimmies.
Americans: Merkins
In Dutch, the nickname for Germans has been “moffen” for a long time. I don’t know what it means or where the name came from. I think it’s considered bad manners to use it now. The Dutch are known as “kazen”, cheeses. (the only food related nickname in my language I can think of right now).
Jimmies? Is that common? I’ve heard Jocks, but never Jimmies.
If they’re not being called cornish cunts, then they’re pasties. If welsh wankers won’t do, then leeks might. Irish imbeciles not politically correct? Paddies probably is. And don’t get me started on the Scots, they send sassenachs like me into uncontrollable rage.
(With tongue firmly in cheek, you don’t want to piss off those red blooded celtic types)
I’ve read that, in the Falklands War, British soldiers would call the locals “Bennies” after a friendly but stupid TV character. When ordered to cease, they changed the name to “Stills” - for “Still Bennies”.
Beware of Doug, a precision. French Canadians are/were not called “Pepsis” by the French, but by English-speaking Canadians. IIRC, at one point Quebec was the only market in North America where Pepsi outsold Coke, thus the nickname. See items 2, 3 and 4 on this page.
Yep, it was “Crossroads”, and the Benny character always had a woolly hat and really rather a woolly brain. 
In my 36 years on this earth as an English-speaking Canadian, I have never once, not a single time, heard or read the term “Pepsi” as a euphemism for Quebecois. I googled it and could find no specific usage of the term by a Canadian EXCEPT in the Urban Dictionary, which is probably the least reliable reference work in the entire history of written language.
I stand corrected. 
Too late.
Aw, someone can’t take a joke…
In Mexico and most of the Spanish-speaking Americas, North Americans are referred to as Gringos, a supposed insult that has a fairly innocent origin. During the Mexican-American War, the invading American soldiers liked to sing the popular songs of the day as they sat around the campfire. (Not having, I suppose, anywhere to recharge their ipods) So the Mexicans would hear the voices singing every night “Green grow the lilacs all sparklin’ with dew…” and a nickname was born.
Another origin version I’ve heard for that term is that the American soldiers wore green, hence: “green, go home.” Which got shortened to gringo, and is not used only in the Americas but in all Spanish-speaking countries. We just don’t do it to their face since they consider it offensive independently of tone of voice. And it’s not North Americans: it’s Anglophones from the US.
In Spanish it’s Germans who are called cabezas cuadradas or cabecicubos, “square heads,” “cubic heads.”
In XVIII and XIX century Spanish, “gabacho” means anybody from North of the Pyrinees and/or those who think “foreigners do everything better”; in XX century parlance it’s restricted to the French. Currently it’s being lost since it’s not PC: we promise not to call 'em gabachos if they don’t trot out that joke about Africa starting at the Pyrinees.
The American uniform in the '48 War was grey.
Pel2na & Nava, I think you both may be incorrect. Here’s what Snopes says on the matter. It apparently comes from the Spanish word for Greek.
That Snopes explanation makes no sense, specially since, in Spanish from Spain, we do NOT say “it’s Greek to me”. We say it’s Chinese. I’ve heard other Hispanics say “me suena a chino” as well.
Well, using Google books, I can find an example from 1835, published in 1839. This obviously predates the Mexican War.
Well the cite they use in the link is from 18th Century Malaga, perhaps they said it there, then but don’t say it now.
A few more from Wiki:
Los guiris, Spanish for anglophone tourists always asking “Where is …?”
Os camones, Portuguese for North Americans, always saying “Come on!”
And my favorite:
A highly local one: Air traffic controllers in New York are reported to call Air France pilots keskidis, for their way of asking each other “Qu’est-ce qu’il dit?” after receiving another rapid-fire transmission.
Not all polynesians are coconuts in New Zealand, some of them are cookies (Cook Islanders) they get quite offended if you call them coconuts not because it’s a racial label, because it’s the wrong one.
My kid has mixed ancestry, I tell her she’s part Krispie (a brand of coconut cookie), as well as about half the other nationalities mentioned here.