Spanning 12 years and multiple flashbacks to unmemorable holiday high jinks, “People We Meet on Vacation” unfolds in vivid colors and mostly foreign locations. Along the way, Alex and Poppy — whose job as a travel writer reminds us how sharp Jameela Jamil can be, even in the minuscule role of Poppy’s boss — acquire and retire romantic partners and perpetuate the inane notion that getting soaked to the skin is some kind of aphrodisiac. Who doesn’t want to have sex while looking like a drowned rodent?