Have an uncomfortable talk with her in front of trusted witnesses. Tell her you don't treat work as a socialization experiment and would appreciate her respecting your boundaries.
...THEN smile...no smirk
No don't do that. That's the petty Patty in me.
But I digress, just let her know you care more about work than pleasing others and you appreciate a professional work environment. People are so irritating with that nonsense. How you gon tell somebody else to do something to make YOU feel good?
If you don't smile, then what? Nobody is required to smile if they don't want to. It makes me wanna have you smile with everybody else except her silly self.
...THEN smile...no smirk

No don't do that. That's the petty Patty in me.
But I digress, just let her know you care more about work than pleasing others and you appreciate a professional work environment. People are so irritating with that nonsense. How you gon tell somebody else to do something to make YOU feel good?
If you don't smile, then what? Nobody is required to smile if they don't want to. It makes me wanna have you smile with everybody else except her silly self.
" thread


. If the genders were reversed and it was some old cac telling the young chicks to smile, see how fast they would have reprimanded him or just flat out gave him the
.
and say it's 'not that deep.' Then you want to discourage and shame other men out of standing up for themselves too. 
I have no response