Who's Your Daddy? is the nineteenth episode of Season 4.
When Dad can’t attend a Squirrelly Scout Festival because he has to work, Timmy magically tries out some of his buddies’ Dads as replacements. You’ll never guess who the substitute Dad he ends up finding is.
After his dad leaves for work before they can go to Timmy's scout troop, Timmy sets out to find another dad to replace him. After seeing A.J. and his dad play with giant mechanical robots, Timmy wishes that A.J.'s dad was his dad.
Wearing A.J.'s signature sweater vest, Timmy then wakes up in A.J.'s room after his Albert Einstein alarm clock goes off. A.J.'s dad then comes in and Timmy asks if he would accompany him to the Squirrely Scout Camp, only to have A.J.'s dad decline his request since it was too dangerous. Instead, he goes virtual camping with his device, much to Timmy's boredom since it wasn't as fun as actually going camping in the wilderness. After his failure, Timmy decides to trade dads with Chester after seeing that his dad wasn't afraid to get down and dirty.
Timmy is woken up by a rat slapping his face with its tail and then Chester's dad drags him to the Dimmsdale Zoo to get some breakfast. Hungry for some cheap food, Chester's dad then grabs several meerkats from their cage, wanting to fry them up for his meal. He then notifies Timmy about another good eating spot: the Dimmsdale aquarium, a.k.a. the All-You-Can-Eat-If-You-Don't-Get-Caught Buffet. Timmy then realizes that none of his replacement dads are working out for him, so he decides to trade his dad with Sanjay's stepdad.
At 5 a.m., Timmy is abruptly awoken by his alarm clock, which loudly plays the Reveille. His stepdad, a U.S. marine, makes Timmy do hundreds of backbreaking exercises. After the crazy workouts, Timmy decides to switch back to his own dad. Depressed that he has no one to go with him to the Squirrely Scout Camp, Timmy is cheered up by Wanda who tells him that maybe he should try to find someone other than a dad. After seeing Mom's resourceful skills, Timmy decides to bring his Mom with him, and they end up winning the trophy at the camp.