I believe that any person who claims they have build self confidence should be able to handle criticism without having a toddler's attitude. Of course that we would prefer constructive criticism, politely delivered, but how often does that happen? We should also be able to dust off any criticism which has the purpose to belittle us and bring us down instead of improving us. A lot of people disguise their envy and malice in form of "constructive" critique. Those kind of people are usually lacking self esteem and they gain power by bringing others down. That kind of "criticism" should be ignored from the get go. It can happen with a stranger, with a boss, with a family member.