I ask what their favorite web site is, and then I give a 1-2 sentence explanation of how it uses a database.
For example, if they say Amazon, I say, "You know how you add something to your cart, and then you check out, and you pay for it, and then you can see the tracking info? You can come back days or weeks or months later and it's all still there? All that data lives in a database. I make that part fast and reliable."
Or if I already know what they do, like if they're a doctor, I give a 1-2 sentence explanation of how they use a database. "You know how you put in patient data, and when the patient comes back, you can pull up their electronic health record and see their past visits? That stuff is stored in a database. Now, you don't need me because your database isn't that big, but take, say, Harvard's hospital system - they have more doctors, and more patients, so they have a bigger database, and they hire people like me to make it faster and more reliable."
I used to cringe when people would say, "Oh man, that part of our system is terrible, it's so slow," and then I realized it was a sales opportunity. So that kinda works out.