A Bad Case Of Diary-Uh! is the seventh episode of Season 4.
After Vicky uses a truth serum to make Timmy spill his deepest, darkest fears, she uses this knowledge to humiliate him in front of his school. Seeking revenge, Timmy wishes for Vicky's Diary so that he can use her secrets against her.
It's another evening with Vicky; She takes advantage of Timmy's well being and forces him to watch movies that creep him out. When Timmy lets it slip that he is afraid of clowns, Vicky uses a truth serum dart to get him to blurt out his secrets; he is afraid of clowns, allergic to oranges, bare feet disguist him, and his fish are fairy godparents. Vicky does not listen to the last part, fortunately for Timmy. The next day at school, everyone is celebrating "Orange Juggling-Barefoot-Clown Day",which is hosted by Vicky, causing Timmy to run for his life, smacking into a door several times. Timmy decides that Vicky has gone too far and wishes for her diary.
Although Wanda rejects the idea at first, Timmy states that Vicky thinks "the pink squirrel looked fat" which enrages Wanda, putting her on Timmy's side instantly. Cosmo also objects, as he too has a diary, but Wanda wants revenge. They try everything disgusting to make Vicky look bad in front of Winston Dunsworth, a British boy that she likes. First they find Vicky preparing to talk to him, about to put on her new perfume. Timmy wishes for her perfume to contain skunk spray. Wanda offers a better idea. The perfume is switched entirely with a skunk. Vicky is disguisted by the smell, but to her, Timmy, and Wanda's shock, Winston loves the smell of skunk; It reminds him and his people of "the hunt". Next, Vicky decides to get her face done by a professional makeup artist. Timmy wishes the artist were a monster movie artist. The artist makes Vicky look like a werewolf. To everyones shock again, Winston loves werewolves, for they also remind him of the hunt. Timmy reads her diary yet again and sees that she will be auditioning for cheerleader, as Winston only goes out with them. Timmy plays irony and wishes for Vicky to blurt out all of her secrets. She hates cows, sucks her thumb, lies, cheats, shoplifts from every store, picks her nose, and puts her snot and boogers in people's history books. This time Winston is unhappy; he doesn't mind the lying and cheating, but adores cows and hates snot in his history book. He ends up with another girl, leaving Vicky heartbroken and Timmy and Wanda satisfied.
Unfortunately, Vicky is so depressed that she can no longer babysit, and Timmy is left with a worse babysitter. He then decides that he must fix things. They decide to read Winston's diary and find out, to Wanda's dismay, that Winston is afraid of the color pink. Wanda is in her pink squirrel form and scares Winston, getting Vicky to save him. During this time, Timmy blurts out how Vicky hates the squirrel, and a suspicious Vicky uses a truth serum dart to get Timmy to reveal that he has been reading her diary. She pounds him and the pink squirrel. Vicky is thrilled when Winston thanks her, but he still won't go out with her because she is not a cheerleader. Timmy, Wanda, and Vicky are left miserable, while Cosmo writes of his adventures in his diary.