She was that. Her bitter marriage (of only 32 days) to actor Ernest Borgnine was well publicized. Merman once remarked that she attended a showing of the movie "Willard" just to see Borgnine eaten by rats.
Several years ago I was acquainted with a waiter, whom I shall refer to as Ray, who worked at a restaurant frequented by Ethel Merman. One evening during one of her rants she bellowed to Ray, "do you know who I am?" In his characteristic "don't fuck with me" style, Ray calmly replied "yes, I certainly do Mrs. Borgnine." Ray told me she then really lit up the place, bringing the head waiter, the manager, and one of the owners to her table. Having done nothing improper, Ray came away from it all unscathed.