Because i'm handsome without smiling ;)

because you have to smile first. which you don't on your profile pic. ;)

it's the law of reflection...

(no, Parisians don't smile in the subway in the morning, why would they? they're going to work. you picked the wrong moment. check again after a huge fantastic concert at Bercy and tell me what you saw.)

I'm french and I smile so.. maybe it's because I don't live in Paris, ahah

Lucas Silva, I think it's not about just smiling without a good reason. It's about the situation when addressing a local person in Paris in the street (asking direction or something) with a smile they will not smile back but keep a serious expression on their face. At least that's what I've noticed in Paris. :)  

haha ...yes I agree  @Laufala