To yawp is to cry out or whine loudly. Don't yawp over spilled milk; just clean it up.
The harsh sound of a yawp is similar to a yelp — your new puppy might yawp from his crate when you put him to bed at night. People yawp too, calling out in despair or victory or anger. The most famous instance of the word yawp is probably Walt Whitman's, in Leaves of Grass. In the section of his celebrated poem called "Song of Myself," he writes: "I sound my barbaric yawp over the roofs of the world.”