who died and made you king

who died and made you king and who died and made you boss — чего это ты тут командуешь?; Чего ты тут командуешь? Чего раскомандовался-то? Кто тебе дал право командовать? Кто ты такой, чтоб тут распоряжаться?

Example: If I am a waiter at work, and another waiter says "Go bring food to that table!" I would say, "Who died and made you boss?"

This expression is used when someone is acting like they have power and giving orders when they don't have the right.

... cf
[throw one's weight about]
[slave driver]
order sb around