I’m not sure when the Bonnie Raitt gray hairs on the right side of my scalp started growing into the skunk-like strip it is today, but it never felt like a nuisance until one night in Hanoi, Vietnam. Rihanna was blaring from the speakers while disheveled-looking travelers were checking in at the front desk. On one wall, a chalkboard listed group tours: “16 amazing days jam-packed with history, wildlife, and adventure!” Nearby, a young man trying to sell his Honda motorbike ($240 or best offer) stood under a disco ball, a “for sale” sign pinned to his chest…