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<p>That’s similar to the “if you can’t tell what gender the person is, assume male, because a woman won’t be offended by being called Mr as much as a man will be by being called Mrs” rule of thumb. But at my house, if you call up asking for either Mr or Mrs MyLastName, you’ll be told there’s no one by that name here, and hung up upon, because I don’t go by Mrs MyLastName.</p>
<p>My kid is little, and her friends address me as “Kid’sName’s mom,” which makes everyone happy. (I’ve had a couple of parents of kid-friends call my kid KidName MyLastName, which really ticks both her and me off, because she has her own last name which is not the same as mine.) My client’s teenage kids sometimes call me MyFirstName, and sometimes Ms MyFirstName, and sometimes Ms MyLastName, all of which are fine with me. College-age kids all call me MyFirstName.</p>
<p>We get “family” museum memberships that cover any two named adults plus kids living at the same address. I put me as the primary member, and my father (who is the backup babysitter and museum-goer) as the additional named adult. Invariably, the membership paperwork comes to Mr and Mrs HisName, which also ticks me off.</p>
<p>There is no universally non-offensive way of addressing another person that doesn’t start with, “how would you prefer I address you.”</p>