Karen

A person who always complains about a simple problem (that is usually cause by someone else) instead of fixing on her/his own and gets angry quickly and seek a third person that has more influence/power to solve the problem for her/him.
A Karen is usually a white middle aged woman

Employee: Boss, there's a karen that wants to meet you. She wants 10 instead of 8 olives on her sandwich but she has already paid for it and now she wants another one for free.