In the 1950s, before he became President, Richard Nixon visited Latin America on a goodwill tour to try to patch up strained relations with the locals. As he stepped out of his plane he showed the waiting crowds the American 'OK' signal and was stunned as they began booing and hissing at him Being unaware of local body language customs, Nixon's OK signal had been read as 'You're all a bunch of arseholes.'
If you travel internationally, the safest rule is to always ask the locals to show you their insult signals to avoid any possible embarrassing circumstances.