I've decided to run with the "5 hazards of..." and make it a sort of Series. :) That said, here are the 5 hazards of having lived overseas:
1. You become a terrible "food snob." It can be as frustrating to us as it is annoying to our friends and family when they go out with us to a foreign-themed restaurant and we moan and sigh about how "un-authentic" it really is. And if the place you lived in was in Europe, your formerly-beloved good old American Hershey's will now taste like chocolate-flavored wax. Of course the positive side of this is how lucky we are for all the fabulous food we have enjoyed! And Americans who spent some time overseas can be great reviewers for restaurants, because we now know what "genuine" food tastes like from whichever country (or at least one part of that other country!).
2. If you still have friends after snobbing it up at the restaurants (LOL), you can irritate them further by commenting how much the weather or landscape or that building reminds you of your former home overseas, or how much you miss going to xyz. It's not our fault--those are just former homes to us, just as you might mention memories of the place you grew up or how your mom did something. But somehow it comes off as bragging when it involves somewhere "exotic," and once again we sound like snobs, even when we truly have no intention of doing so.
3. Ironically, while you can easily annoy so many people, sometimes you won't know ENOUGH to satisfy other people. After all, you didn't go there as a tourist but actually lived and worked in the other Nation. As a result, you may or may not have done the usual touristy things. SO many people have asked us "oh did you visit here?" No. "Did you do this?" No. "Did you buy that?" No! We were a little busy trying to just live, and raise our family. And if you are like us, and were living overseas in some sort of "American bubble" (in our case the military community), you may not even be proficient in the language, which really annoys natives you meet from your former home. Yes, we probably should have tried harder, and yes it is embarrassing to say we lived 4 years here and 6 years there and never learned either language (or only enough to get by). :-/ But it is what it is, and no one can go back and do it over. We aren't the only lazy expatriates who don't learn the language of the host nation. On the bright side, we have enormous sympathy for foreign-language speakers here in the United States, and are much more likely to support subtitled signs and menus, etc.
4. It becomes harder to clean out your old things, because you never want to get rid of those items that remind you of your former home. :) It's sentimental value, yes, which is something we share with everyone, but it's more than that. When a break a coffee cup, it's no big deal to get another one. But when am I ever going to go to another Christmas market in Cochem, Germany? I can't possibly throw out THAT cup; we must try to fix it!! I don't care if that pen is dry, it says Okutama on it in japanese and I'll never ever be able to get another like it! No honey, don't open that last bottle of wine--it's the very last one from Georgia (the Country, not the State!).
5. You will miss it forever. A little bit of different States in the U.S. will "rub off" on you as well, of course, but most States aren't as much different from one another as the other Countries where we have lived... and they are much easier to revisit. Many Americans who have lived overseas will never again step on the soil of that other Nation that was their home for a time. And of course even if you do, it won't be the same. Then again, neither are you the same. And that makes it worth it all.