Late Saturday night, Bridget Todd, a writer, activist, and former lecturer at Howard University, tweeted at taxi dispatch startup Uber that she'd been choked by the driver she'd ordered on Uber's smartphone app—apparently because he was angry at her interracial relationship. Uber CEO Travis Kalanick's response, in an emailed warning to his PR team: "make sure these writers don't come away thinking we are responsible when these things do go bad…"