This is not good time to warn people.
We just started mainstream crypto phase. Its too early to see them become worthless.
It will have lot more demand in 10 coming years. You'll see.
When should I warn my fellow computer nerds?
When its to late?
Ok mr satan.
Also, normal currencies like USD and EUR are also worthless.
Buy real stuff, sell your coins and buy silver and gold, apartments, houses etc.