Japan's prime minister, his poll numbers sagging over a row with Washington, may have caused his popularity to dive even further among fashionistas with a garish 1980s-style shirt.

Yukio Hatoyama donned a long-sleeved checked shirt designed in large blocks of red, blue, yellow, green and purple during a recent meet-the-people barbecue promoted as the "Real Hato Cafe".

Fashion critic Don Konishi wasn't laughing and lashed out at the premier's fashion crime in a national magazine and on the airwaves.

"Is anyone able to stop him wearing such a thing?" Konishi asked in an irate commentary about the offending shirt.

"It's too old. It's out of date. He doesn't have his own style."

The PM scored a landslide election victory last year, but his poll ratings have since fallen into the low 20s due to a row over an unpopular US airbase and criticism of his sometimes dithering, collegiate style.

To Konishi, the shirt was the final straw as he predicted the demise of Hatoyama's Democratic Party of Japan (DPJ) government.

"It seems the DPJ is over with this shirt," he said.

Hatoyama - a former assistant professor and the scion of a powerful political dynasty - was once nicknamed the "alien" by his fellow party members for his quirky appearance.