My Dad vs. Your Dad is the third part of the 13th episode, serving as the season 3 finale. It aired on September 20, 2002. In this episode, Dexter and Mandark's fathers Dad and Windbear both get into a fight after diffusing their children.
The episode begins with Dexter and Mandark in an old western standoff with giant robots. Dexter and Mandark then activate missile launchers and they blast them at each other. They both gracefully dodge every shot that has been blasted at them and neither of them is hurting the other, so then they result to using bigger robots. They both start fighting each other with them but it they are too evenly matched and their fight is going nowhere. Eventually, they both give up and agree that they are too evenly matched one on one. Mandark tells Dexter that his dad could beat his dad in a fight. Dexter replies to Mandark saying that his dad could beat his dad in a fight. They both agree to get their dads and use them to help them fight each other and they both run home to get their dads to help them.
Dexter starts telling Dad about all of the things Mandark his to him and Mandark tells Windbear about everything Dexter did to him. Windbear tells Mandark that fighting in wrong and he should not be doing it with Dexter. He says that to grow up being a wise and successful person, he must be peaceful and not result to acts of rivalry and war. Dexter's dad tells him that what Mandark was doing is something that kids do all the time and that he should just ignore it. They both seem to not care much for their fight until they tell their dads about how they both bet that their dads could beat them in a fight. This raises their interest and they go to talk it out.
Dad and Windbear meet up at the park with their sons and they talk to each other about it. They both tell their sons to say their sorry and they both let out an insincere and lazy apology to each other. Dad and Windbear talk about how ridiculous it is that they would believe that they would ever result to fighting. They both jokingly make politically incorrect insults to each other about how neither of them could beat the other up. At first, they seem to be perfectly fine with what they are saying to each other, but after a little bit, the insults get out of hand and they actually get angered toward each other.
Their argument escalates to the point where they might get into an actual fight until Windbear stops it by making the peace sign to say that he wants to resolve the fighting with peace. Dad believes it at first until Windbear stabs him in the eyes with his fingers instead. They finally break out into battle and they start beating each other up. Dexter and Mandark feel happy because of them seeing their dads get into a fight like this. Dad runs off and Windbear chases after him.
They go to a picnic area and start throwing food at each other. Dad throws a ham on rye sandwich at Windbear and then Windbear retaliates by flipping burger patties at his face. They both start chucking food at each other. Windbear runs off and Dad chases him to a pond. Windbear gets into a paddle boat and paddles off and Dad gets into one too and paddles after him. They are both slowly going after each other. Dad picks up a duck and throws it at Windbear and they both start throwing ducks at each other. Then, Windbear's boat starts sinking and Dad swims off and Windbear chases after him.
They both get into their cars and start ramming them into each other. The fight that they are in is going nowhere and just keeps getting worse and worse. Dexter and Mandark are watching and then Dexter mentions that their dads are too evenly matched just like they are. Then Mandark bets has his mom could beat up Dexter's mom and Dexter bets that his mom could beat up Mandark's mom and they both start insulting each other while their dads keep smashing their cars into each other and the episode ends.