It's not a usual one. There must be context somewhere.
2011年4月8日
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cup,
it means who is somebody doing anything? hahahahaha!
2011年4月8日
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nice picture, who let the dogs out :P lol!
2011年4月8日
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There is a popular song in the US called "Who let the dogs out". In fact the phrase is repeated so many times in the song, it is hard to get it out of your head. I guess "who let the jam out" is a play on word after this song.