It's a slightly old-fashioned American expression for a failure, or anything that's useless or disappointing. Here's some information on the phrase: http://www.word-detective.com/2012/06/turkey-2/ Is it common? Not really. Its main use seems to be as a word-play headline. If by 'decent' you mean is it polite, then it's not exactly complimentary, but it isn't vulgar either.

It is a mild way of saying that a person or a thing (such as a theater production) is a failure, or inept, or stupid. It is not vulgar. But it would be impolite to say it within hearing range of the person you are referring to.

"Don't let the turkeys get you down." [See row 2] http://dragonfire1.50megs.com/Boynton/mugs07.htm