Infidelity. In-Laws. Friendship. These are just a few of the categories that help keep the Dear Sugar inbox organized. But every once in a while, we get a letter that doesn't fit neatly into any category. This week, the Sugars discuss a handful of those letters in rapid-fire fashion -- from a woman whose mother-in-law might be faking an allergy to her cat, to a woman whose identity was stolen...by her own sister.