Joke insult in Japanese?
 

Alright, so one night with my Japanese teacher,
my friend and I are going on reading the Japanese text
and my friend mixes up 「る」 and 「ろ」,
so I say, "Hah, you're such a Polack!"
And then it hit me, is there an equivalent in Japanese?
So I asked him and he said, while he was in Japan,
only with his closest friends, you could joke around
and instead of calling someone a Polack, they would use...
Korean. As in, "Ah, you're such a Korean!"
Is that true?

No. There is no tension between Poland and the US, so it's a dumb joke based on an outdated stereotype. Most Americans have never met a real Polish person, and if they did, they wouldn't say something like that.

Up until the most recent generation there has been high tensions between Koreans and Japanese, but at the same time, many Koreans live in Japan (often 2nd or 3rd generation).

To make a long story short, it's a racist joke that is reserved for your friend's "closest friends" but not one that I have ever heard or would expect to hear out of the mouth of any of my Japanese friends. If someone says something stupid, you call them "baka" not "korean".

I cannot believe your teacher said that. No educated Japanese (or really any Japanese) would say "Ah, you're such a Korean" in that kind of a situation.

US people never meeting Polish people...
Uhh, come to Chicago.
List of cities with highest Polish populations:
1 - Warsaw, Poland
2 - Chicago, IL, US
Yeah, I go down the street hearing Polish all the time, haha.
And around here, they're just jokes that've stuck.
Even Polish people use them (the ones I hang out with at least).

That is one I have certainly never heard. I seriously doubt that most anyone would associate "Korean" with a joke insult either. They`d probably just respond with "No, I`m not Korean."

There was a bit of a hit with something along those lines (欧米か？) from a stand up comedy routine. I can`t really imagine anyone using it outside of imitation though.

Go ahead and make make fun of Polish people if you want, but as Nagoyankee said, that isn't a joke Japanese people use, so no one would laugh in Japan if you said it.

No, no, no.
It's not used as an insult to Polish people
really anymore. It's just used now as a
general term for someone doing something
stupid.
But thanks for clearing it up for me, that's
why I asked the question. (^_^)

But then, what kind of jokes and stuff is funny in Japan.
'Cause I know I LOVE insult comics,
like Lisa Lampanelli, Sarah Silverman, etc.

still where all of this came from ? I am polish and i feel kinda offended..

Before blonde jokes were blonde jokes, they were Pollack jokes. It was probably from a very old stereotype that doesn't even exist anymore (in the US...except apparently in Chicago.)

When I lived in Japan, I heard a kinds of sayings and jokes about the Chinese. I also heard words like Sankokujin. This stuff is evertywhere in the world. I've heard guatemalans poke fun at Mexicans. Polock (and other euro jokes) stem from stereotypes from world war II.

Heres a good/stupid multilingual joke: Did you know shrimp have special vitamins? Vitamin AB (ebi).