The phrase 'Much Ado about Nothing' is used when someone is overreacting and makes a big deal of fuss over something unimportant.
Example of use: "Some people make a big fuss about which seat they'll get on the plane, but as far as I can see it’s much ado about nothing, since everyone will get to the same destination at precisely the same time."
'Much Ado about Nothing' is the title of a well-known play by Shakespeare (1599). The phrase assimilated into the English language and to this day is still used in its original form.