Your better alternative would be saying " a lucky duck " which carries in itself quite another meaning for everyone, included varied foreigners. And it scarcely renders any shade of offensiveness.

To call someone a "dog" is not good. To call someone a "lucky dog" is kind of backhanded congratualtions - you're happy for them, but slightly jealous. Unless you know the person really well, don't use slang... even if it's written in a book. Books won't save you here.

Actually, the term "lucky dog" exists and was used extensively at one point. It is not used so much anymore, which is why some people don't recognize it. Said in the right way and the right circumstances, it is not considered an insult. It is (was) used when a person runs into some luck or good fortune. One of their friends might say it jokingly to indicate that the friend is a little envious of their good fortune. "I won the office basketball pool last week. It was a hundred dollars." "You lucky dog! I assume you'll be buying the first round at the bar when we go out!" [Note: This is why I am very careful with idioms and slang when I am talking with foreigners. There is much that can be taken wrongly.]

In English, we usually say "You're a lucky dog!" if your friend just had an unusual piece of good luck -- if they won some money or just had something good suddenly happen to them. A conversation might sound like this: A: I was just had my short story published! B (smiling): Oh, you lucky dog! I've been trying to get published for years! And you have published before me! The problem is that different cultures don't like being called a dog. Most of the time, it is an insult to call someone a "dog." "That girl is a dog" usually means that she's ugly. "The movie was a dog" means that it wasn't well-liked. We call a sneaky person a "sly dog", or a lazy person a "lazy dog." So there are many places where "dog" is an insult. In fact, "lucky dog" is a friendly insult -- you are calling the person lucky, but there is a hint of an insult in "dog" -- because the luck didn't happen to you, but to your friend! Be careful when you call someone a dog!

It's like calling someone a dog? The term 'lucky dog' doesn't really exist in English but if it did I imagine it to be offensive. Its like sayings someone looks like a canine, they're aggresive, furry, animalistic, smelly ...? http://bit.ly/ekO14i