Season 2 has been a bit iffy, but this was an excellent episode. Like Joffrey with the necklace, he could be luring her in to destroy her. Pointlessly antagonizing people means giving them a reason to strike back if they ever have the chance. Being nice to them can be profitable. It's not easier to go along with Joffrey, it's stupid, and Tyrion's motivations are personal rather than based on kindness towards Sansa - he wants Jaime back and he knows that keeping Sansa relatively safe (that is, not beaten too publicly, he doesn't interfere before that) helps Jaime's odds of surviving. And book Tyrion does end up agreeing to participate in Sansa's abuse when he decides to marry her to get Winterfell, doesn't tell her about that plan until the day it's carried through, chains her to the family that has abused her and a marriage that will keep her in danger of being raped by Joffrey, gropes the frightened 12-year-old, and proceeds to whine about how she wouldn't kneel to save his pride or become his loving fantasy girlfriend, because obviously he's the one suffering in that situation. Sansa is actually being perfectly intelligent by not trusting Tyrion since his goals are the opposite of hers (they involve the defeat of her family and later the claiming of Winterfell through marrying her), and it's not trusting him that allows her to escape her forced marriage, Lannister abuse and a city where she has no one interested in prioritising her safety or even in helping themselves by helping her. She sees what Tyrion fans can't, that he's not on her side.