Each thing 'everyone knows' by the time that they are an adult, you have on average 1o,ooo people in the United States of America hearing about it for the first time.

Fraction who have heard of 'it' at birth = o%
Fraction who have heard of 'it' by 3o = 100%
United States of America birth rate = 4,ooo,ooo per year
Number hearing about it for the first time = 1o,ooo per day

So, if you make fun of someone who admits that they don't know of something, or that they have never heard about something you train them not to tell you when they don't know about something.

And, of course, you miss out on all the fun. Because what is more fun than seeing the face of a lucky someone who just realized how amazing Diet Coke and Mentos togeather are?

Just a thought.

sourced- xkcd