In Malayalam/Indian, there's a saying "Thala Irikkumbol, Valu-attaruthu!", which literally translates to:
When the head is present, tail should not wag.
It means that one should not act out of turn in the presence of one's superiors.
Mafia bosses A and B discussing stuff; a low-ranking member M chimes in interrupting them; A puts a bullet between M's eyes saying something-cool-here.
I'm not limiting answers to mafia style, though that would be cool.
What are other English idioms equivalent to this?