I believe the answer to your question would be when the big supermarkets accept some form of btc for their goods.
Aside from that. people will be comfortable in using bitcoin when the right time comes and that right time is when all the people living in the world will have an agreement in legalizing the bitcoin in all over the world. People will be comforatble in bitcoin if they will fully understood the mechanics and system of it and how it affects their daily lives positively. I hope that day will come soonest.
Agree. Legalization of bitcoin currency is the great factor that people would become comfortable using of it. Because as of today there are many countries which are not aware yet the existence of cryptocurrency investment.