Stumpy and Quack Quack are best friends, and they often hang out with each other. Sometimes, however, they get into fights, like in "Let's Play Me-Me-Nopoly" when they fought over who got to sit on the couch.
Stumpy enjoys hanging out with Quack Quack, and they do all sorts of crazy things together. Sometimes, Stumpy asks Quack Quack for help in understanding something or learning something new. If Quack Quack refuses to give Stumpy what he wants, Stumpy will decide to break off their friendship until Quack Quack gives it to him. A notable example of this was in "Let's Play Guess Who!" when Stumpy wanted Quack Quack to teach him a technique which he refused to teach him. Eventually, Mr. Cat set Quack Quack on fire, and Stumpy refused to put out the fire unless Quack Quack taught him the technique, so Quack Quack wound up teaching it to him. In "Let's Play Teachers", he gets angry at Quack Quack for being smarter than him, and he later beats him up so he can get sent out of class. In "Let's Play Paper Balls", Stumpy joins Mr. Cat in torturing Quack Quack (and Kaeloo) with magic paper balls for no reason. In "Let's Play Prince Charming", Stumpy says that he and Quack Quack are just friends, but in "Let's Play Hot - Cold" he seems to fall in love with him, but quickly gets over him in favor of Ursula.
Quack Quack is usually nice to Stumpy, but they fight on occasions. In "Let's Play Dubbing", Quack Quack agrees to alter Stumpy's personality to match Mr. Cat's, resulting in Stumpy torturing him. Despite the fact that the whole thing was Quack Quack's fault for agreeing to change him, Quack Quack gets angry and turns Stumpy into a sheep. In "Let's Play Baby-Sitting", he gets angry at Stumpy for forcing him to act like a baby and then doing things like feeding him spinach, but by the end of the episode, he feels so sorry for Stumpy that he decides to go along with the plan. In "Let's Play the Very Special Episode", he expresses regret for ever making fun of Stumpy.