"The thumbs-up gesture is commonly used in many cultures to signify a job well done. However, if it is used in Australia, Greece, or the Middle East — especially if it is thrust up as a typical hitchhiking gesture would be — it means essentially “Up yours!” or “Sit on this!” The thumbs up gesture can also create some real problems for those who count on their fingers. In Germany and Hungary, the upright thumb is used to represent the number 1; however, it represents the number 5 in Japan. "
Huffington Post.