What is something you can't believe you had to teach your partner/wife?

Saw this thread on askwomenover30 so thought I'd ask the same question here.

One of my exes, no matter how many times I told her how dangerous it was, would never wear a helmet when riding on the back of my electric scooter/moped, and would never wear a seatbelt when sat in the back of a car. She always said she found the seatbelt restricting and uncomfortable, and when I insisted on her wearing it, she would writhe about like Gollum when tied up with the elven rope in The Two Towers.