Just show them how much profit you made form bitcoin.
If they see that they will immidiately join and understand what bitcoin.
yup this make sense , show them the historical data of bitcoin from it's humble beginning up to it's current value today , every year bitcoin was undeniably increasing in value , show them how much they can profit in less than 6 months if they can see that the return is good they might think again on investing on bitcoin.
It depends upon the nature of the people which varies from person to person and I think it is also dependent on the age because the young pool are very much familiar internet and computers so they can very easily be convinced while the aged people will be so hard to be convinced about the profitability and other merits of bitcoins.