I just read this good article about avoiding taboo behavior when traveling. I’m not talking about seriously bad behavior (getting in fights, committing crimes, going to jail). This is more about things you might do by accident that could offend people (like holding your fingers in a certain way that seems harmless but in fact is insulting people’s mothers).
The article is pretty short on specifics, but in general it gives some good practical advice. The main point is that you should just know you’re in a different culture, and you should try to be aware of what feels right and wrong. Feel free to ask a local if you’re not sure about something, and do a little research before your trip. It’s nice to know in advance if there are any things to keep in mind for the countries you’ll be visiting. For instance, it’s frowned upon to blow your nose in public in Japan, China and France—who knew?
As far as research, here's a nice detailed overview of the dos and don’ts of body language in various European countries (with links to other parts of the world). It’s written for businesspeople, but the tips seem pretty universal (don’t slap someone on the back in Belgium, definitely don’t give the “A-OK” sign in Spain).
That all said, I’m of the mind that people are generally forgiving when it comes to visitors. As long as you give the (hopefully genuine) impression that you’re in their country to experience their culture and broaden your perspective on the world, I think they can let a little nose-blow slide.
Photo: Mr. Mystery via Flickr