Barack Obama

In this May 22, 2009 file photo, President Barack Obama fist bumps Chauncy Lorrell Gray, from Chicago, as he approaches the stage to receive his diploma at the United States Naval Academy graduation ceremony in Annapolis, Md. The familiar knocking of knuckles spreads only one-twentieth the amount of bacteria that a handshake does, researchers report. That’s better than a high-five, which still passes along less than half the amount as a handshake. (AP Photo/Charles Dharapak, File)

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