With experience, you get a "feeling in the water" as to whether it's appropriate to engage in a bit of banter - who the airline/crew are, what sort of flight it is, are they under post take off pressue etc.
When I'm training Atco's, I have a zero tolerance of the trainee engaging in banter, that can come later when they know what's what.
But otherwise, pleasantries and sharp responses are welcome when appropriate so long as they follow the "stand up, speak up, shut up" phrase book.