I’m Elena, 35, married to Nick, 36. Two weeks ago, I fell through a chair at my mother-in-law Laura’s 63rd birthday. The splintered wood wasn’t the worst part—it was her cruelty. Laura had “invited” us by demanding we bring food, drinks, and a boutique cake, plus a joint gift: a 55″ TV. She scoffed, “I thought you were getting the...