Comes from the song Hey Ya! by a group called Outkast intoning women to shake it out on the dance floor. Refers back to when people used to wave around or fan their instant photos in order to dry them. The popularity of this song/phrase caused the Polaroid company to put out a press release warning people NOT to shake today's Polaroids because it would ruin them.
She knew how to attract men: she would get out on the dance floor and shake it like a Polaroid picture!
What the people do in the music video for Outkast's "Hey Ya."
"I'm going to be in the video for "Hey Ya" by Outkast... what should I do?"
"Shake it like a polaroid picture!"