Recently a potential partner arrived in China for detailed discussion and negotiation about a long term partnership.  The Chinese are great hosts with extravagant welcoming banquets and small (or not) gifts like Hangzhou's famous Longjin green tea or locally produced silk items.  Understanding this tradition our guests came prepared with several mementos.  One of these was a green (their company color) hat complete with logos and special messages.  Well, there was great reluctance to accept such gifts but our guests persisted in forcing acceptance.  Of course they did not realize that in China "green hats" or Lu Maozi have a special significance.  One is said to have a green hat when your wife has been cheating on you.  And in fact foreigners wearing green hats in public will receive more than their fair share of strange looks and stares.

It just goes to show that there's alot to learn.  I checked all my Chinese etiquette books and could not find the "green hat" taboo.  Of course the only reason I knew is because once I'd been that foreigner parading myself around town with a green hat.