I used to start with explaining blockchain, but most people get dizzy real fast. I think sending a few sats over lightning as a demonstration can pique curiosity, then go from there based on the person's interests. If he has a tech background blockchain is actually fairly straightforward, you at least don't need to explain what public key cryptography and hashes are. If not, economics is a good approach. Most people don't know much about the topic but you can take angles they can relate to - currency the government can't inflate or easily confiscate, etc.