Last week in his home state of Michigan, Mitt Romney joked that everyone there knew him and no one ever asked for his birth certificate. The press and the left affected shock that Romney would even make an oblique reference to theories that President Obama was born in Kenya instead of Hawaii. Ironically, their shock and outrage blinded them to just how cutting ROmney's joke really is.
Romney was probably responding to numerous allegations by the Obama campaign that he is out of touch or just "strange". He was saying "I grew up here." and "I'm one of you."
The cutting part is his implication of why the birther conspiracies are still around. He was reminding us that Obama is exotic. His father is from a different country and he was raised in Indonesia. Romney was saying "I'm like you. It's Obama who is the outsider."
There probably would have been a much greater outcry if people had caught that meaning. It could easily have been critisized as being racists. Instead they stopped listening when he mentioned the birth certificate. By repeating the joke, Romney's critics are spreading his message.