Light hearted!
My mum refuses to learn the difference between the WiFi and mobile data. She runs her data down at home (messing around with settings and accidently turning off wifi) and obsessively hounds waiters/baristas for WiFi codes when we are out! I keep telling her she is paying for data and she can use it!
What is something your parents can't get their heads around?
Also She'll also hopefully never learn it was me and now my sibling who dinged the car twenty years ago!