In college, I translated Romantic poetry into Tolkien Elvish. For fun. I had a full binder of Elvish to help me, and I had to make some guesses at some words, though they were rather educated.
When arguing with my sister that her daughter can't be CM2 because her initials are CMCM. CM2 would be C2+2CM+M2.
Nobody in my family will play Star Wars Trivial Pursuits with me either. Then again, I refuse to play with my boyfriend.
When I started my job we had to create fake files in the system to learn how to use it. They had to be obvious fakes, so they wouldn't trigger anyone else to think they were real and get the compliance department involved. I realized that I couldn't use any of my fandom names as fakes because nobody else would recognize them, so I reverted to Sherlock Holmes. Then people still didn't recognize that it was fake.
The biggest actual argument my boyfriend and I have had was whether to go to PAX or D*Con. It's a moot point this year because we can't afford either, but we've each made some pretty strong arguments for our own side. We'll see how next year plays out.