My perceptionn or thoughts on "Be the person that can smile on the worst day" is that be a person who can smile in any stuation even though that day isin't the best . (This is my opinion on what it means and I hope I could help :D )
I think this means be happy in the darkest moments because Auggie is always happy even thought people make fun of hum for the way he eats and how he looks he doesn't take this to heart because he really doesn't care what they say
