It's A Wishful Life is the tenth episode of Season 5.
Timmy tries to do many good deeds for people, but nobody appreciates his work. Angry, Timmy Turner wishes that he had never been born and therefore, becomes nonexistent. Jorgen Von Strangle shows up and shows Timmy how much worse, or better, everyone's lives would be without him. Jorgen tells Timmy that unless he finds somebody whose life is worse without him, he'll be sent to a place where godchildren go when they wish that they were never born, so Timmy tries to find somebody whose life is worse without him.
The episode opens with Timmy Turner doing good deeds for various people hoping to get praise, including painting scenery for one of Mr. Bickles' stage plays, giving A.J. a new high tech computer, cleaning Mr. Turner's and Mrs. Turner's garden and cleaning Cosmo's and Wanda's fish bowl. Instead of praising him, or even thanking him, every person complains that it's not good enough and in fact several times heavily criticize the job he's done, with the fish bowl actually justified as it's still very dirty indicating laziness.
Angry over the treatment, Timmy wishes he were never born. Wanda reluctantly grants the wish, sending Timmy to an alternate timeline without him. Jorgen Von Strangle appears in this alternate timeline and shows Timmy that everyone is indeed better off without him. For example, Chester now lives in a triple wide trailer and has Cosmo and Wanda as his fairy godparents (and uses their magic for many selfless acts, unlike Timmy), A.J. has a full head of hair, and graduated to college (mainly because Timmy is not there to drag him down), the Turners had a daughter who is better than Timmy alongside wealth, Vicky has a job supplying laughing gas to Dr. Bender's patients, Mr. Crocker is not obsessed with fairies, has a full head of hair and a muscular body (while his ear is still on his neck), and Francis is no longer a grey skinned bully, but a tan skinned football player who actually helps weaker kids instead of bullying them. Jorgen tells Timmy that unless he can find someone whose life is worse off without him, Timmy will have to go to "a place where all kids who wished they were never born" go.
Timmy at first tricks Jorgen to throw him in (even though Jorgen wishes to further humiliate Timmy by showing him other people better off, even Elmer, who no longer has his boil), but Timmy returns with Vicky's laughing gas and makes Jorgen laugh so hard he falls into the pit. Timmy is able to grab Jorgen's wand, however upon reflection, he does decide that everyone is better off without him, and offers to voluntarily go to the place Jorgen describes. It is then that Jorgen reveals this has all been a test, or rather a lesson, to teach Timmy that good deeds are not done for praise, but because it's the right thing to do. Jorgen, then, returns Timmy to the correct timeline with Timmy taking Cosmo and Wanda's fishbowl to clean it up. Cosmo and Wanda note that his attitude seems to have changed for the better.