Explain to them that Bitcoin has several advantages:
- It permits direct transfers of funds from one person to another, with no middleman (bank). This eliminates the need to trust this third party, and eliminates the fees that they charge.
- It cannot be forged/counterfeited! This is not true of any fiat currency, or even gold.
- It cannot be inflated at the whim of any government or bank. Inflation occurs when the quantity of a currency is increased, either by simply printing more (or doing the equivalent electronically), or through a process called fractional reserve banking. Find out more about this here.
- Transactions cannot be reversed -- they are final. Once a merchant receives bitcoin funds, they cannot be taken back without his permission.
- It has the essential qualities that a currency must possess, some to an extent never before seen. It is divisible to any extent, it is completely fungible (every bitcoin in indistinguishable from every other in value), it is portable as no non-cryptocurrency is, since it can be sent anywhere as easily as an email or text message (imagine the problems sending $10 million in gold to Zimbabwe).
- It obviates many of the needs for banks, since you can safely keep your money yourself (once you follow some important security guidelines).
- It does not require identification of agents in a transaction, thus eliminating the major cause of identity theft.
If you manage to convince them this, also help them visually by explaining them how it all works, from creating a wallet, sending BTC and send them some small amount or buy something from them for BTC if they are willing.