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You Use Your Husband's Special Sensitive-Gum Toothpaste
Even though your gums are healthy and hardy—save for when you use his toothpaste and feel a weird, sparkly tingle throughout your mouth. This also applies to using your roommate's dandruff-fighting conditioner (when you don't have dandruff). Unlike other life challenges—i.e., saving for retirement, getting the garbage disposal fixed—which may require MIT-level solutions, this one's easy: a trip to the drugstore for over-the-counter products that don't cure what doesn't ail you—such as plain old toothpaste.