tell them a few examples of money waste.

EG 4 years ago car fuel cost $X per gallon/litre.. now it costs more
4 years ago a loaf of bread cost $X.. now it costs more
4 years ago milk.....
4 years ago car insurance.....


now tell them bitcoins..
4 years ago 1 pizza cost 5000 btc. now under 0.2btc
1 years ago filling up your car would cost 20BTC (20 gallon tank) now it costs 1BTC
add more examples

then tell them about banks giving just a couple % interest on savings per year which does not cover cost-of-living inflation. yet bitcoin potentially gives you back more fiat after a year.

yes it is a risk. but the next thing to say is.

"ok mom and dad, instead of buying me these $100 nike footwear, how about i buy a $20 pair of footware and use the $80 in bitcoin.. seeing as its thn not classed as a loss, due to the money having been spent otherwise. what is there to lose"

then find other examples. EG walmarts own brand foods instead of brand named food and use th savings towards bitcoin