What's extremely offensive in your country, that tourists might not know about beforehand?

This question was brought up a few day's ago on Reddit.  Some answers that were mentioned that tourist need to know are:

Thailand, Don't touch people on their heads, it is the highest point of the body so therefore it's the most respectful part. Also never point your feet at a Buddha statue, it's considered very rude.

Also, if you step on money, you'll be thrown in jail, it has the king's face on it and disrespecting him in anyway (like stepping on his image or saying you hate him) will get you a 1 way ticket to a not very nice prison.

When I lived in the Middle East showing the bottom of your feet (like when your legs are crossed) was offensive, saw expats do it all the time though

In Brazil,

The "OK" thing americans do with their hands means 'fuck you' 'Shove it up your ass'. So don't do it.

Ronald Reagan committed the same mistake.

In Germany, doing the Hitler greeting, saying 'Heil Hitler', and the Swastika are illegal here. It's very obviously very inappropriate to visit Germany and pose with your right arm raised for photos, especially when visiting a historically or culturally important place, and yet tourists keep getting into trouble because of this.

When you visit a foreign country be sure to research the local culture so you don't offend any one. You're representing your country, make sure you leave a good impression. 
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