An empty plate means different things to different cultures; in India and Japan, it's important to finish the items on your plate in order to let the host know you enjoyed the meal. However, in China, it's considered rude and means that you weren't fed enough. And in Bedouin cultures, they'll keep serving you coffee if you finish your cup, until you shake it before handing it back to them to indicate that you've had enough.
The moral of the story? Always research customs before you travel. That way you don't offend people, like your cousin Jeff at Thanksgiving last year. Also you can become revered, like your cousin Jeff anywhere else in the world, apparently.
Adam Lapetina is a food/drink staff writer at Thrillist, and was totally the person who introduced Pizza to Bagels back in the day. Read his musings on Twitter at @adamlapetina.