Another one for Deborski's list: Russians -- or at least Russian men greeting other men -- will insist on shaking hands EVERY TIME they see each other. Americans, generally, shake hands as a greeting only on first making acquaintance (or if they haven't seen each other in quite a long time -- but not every single time they say "Hi" to friends).

So my friends Sasha and Dima would want to shake my hand, and I'd be thinking, "What, again? I just shook your damn hand yesterday, dude! I haven't forgotten who you are in the past 24 hours!!"

On the other hand, it makes no difference to most Americans if you shake hands across the threshold of a door -- but this is a big no-no in Russia!

In fact, you never do ANYTHING через порог -- "across the threshold" -- whether it's shaking hands, saying goodbye, giving/receiving a gift, etc. And a Russian-American immigrant that I know is a big fan of Halloween in general, but she says it still makes her uncomfortable when she sees her non-Russian husband (or other Americans) giving the trick-or-treaters their candy "across the threshold".