Here’s a short list of recent mother/adult child comedies: “The Guilt Trip” starring Barbra Streisand and Seth Rogen, “The Meddler” starring Susan Sarandon and Rose Byrne, Ricki and the Flash starring Meryl Streep and Mamie Gummer, “Peace, Love & Misunderstanding” starring Jane Fonda and Catherine Keener, and “My Big Fat Greek Wedding 2” starring Nia Vardalos and Elena Kampouris. Know what they all have in common? They are unwatchable.