As a stereotypical INTJ, my default expression is the "death stare" (as my wife tells me). It just means I'm thinking, nothing malevolent. Smiling is just exhausting. I can't do it on command. And no offence, but I get particularly annoyed by workplace situations where men demand that women smile. Another male (someone known for low-level harrassment) once said that to a female member of staff in my department in front of me, and I came very close to discovering how many muscles it takes to punch someone in the teeth (I opted to tell them not to speak like that to my staff instead - smiling is not a requirement of television scheduling).

Still, I'm not opposed to your sentiment per se, particularly with regard to kindness towards those in service jobs. I've often said that rather than national service, everyone should have to work for a time in a supermarket, or in a cafe, or somewhere involving customers, just to gain proper sympathy for those working there.