CAMBRIDGE, MASSACHUSETTS — A Saudi, a Japanese and an Indian go to a bar. But this is not a joke. An eager American, late for his meeting with the three, arrives. They are in Milan. A problem presents itself: how does the American greet them?

He could kiss the Saudi, bow to the Japanese and press palms before the Indian; but that may be a bit much. He could play the American card and just shake their hands. He could do the Continental European air kiss, since they’re in Italy. Or, like many others in this situation, he could just stand there awkwardly and hope that someone else knows the protocol.

It is difficult enough pivoting between the two, three or four kisses of France; between half-hugs and handshakes in America; between the semi-bows and 90-degree capitulations of East Asia. Around the world, at industry conferences, corporate retreats or fashion weeks, globalized souls meet in globalized environs and wonder whether to do it your way, my way or the local way.

President Barack Obama, a son of blackness and whiteness, of Kansas and Hawaii and Indonesia and Illinois and Kenya, illustrates the predicament. He fist-bumps his wife and the occasional American soldier; merely shakes hands with Republican rivals and with anti-American leaders like President Hugo Chávez of Venezuela; does the fraternity-style half-hug with some colleagues; bear-hugs the occasional citizen-voter; air-kisses Secretary of State Hillary Rodham Clinton; and has stirred fury for allegedly bowing too low before British , Saudi and Japanese monarchs.