Nearly everyone knows a person like the character Kieran Culkin plays in A Real Pain, the story of two cousins who trek to Poland to connect with their Jewish roots, and with the past of the grandmother they’ve recently lost. Culkin plays Benji Kaplan, a likable layabout who comes off as loose-limbed and laid back, the kind of guy who thinks nothing of advancing a brick of marijuana to his hotel; upon check-in, he picks it up as if it were no big deal.