The Hall of Infamy is a large room inside Cosmo and Wanda's castle. Unlike the Hall of Fame, which is also in the castle, it does not feature pictures of the best godchildren but rather it features pictures of the worst, especially for making secret wishes.
Timmy, mistaking it for the Hall of Fame, wished three of the children out of their pictures - Pierre, Maryann, and Sammy. They quickly revealed to Timmy that he was in the wrong room, and then Maryann tricked Timmy into giving her Cosmo's wand before going after Wanda's. Of the three, Maryann arguably was the worst, or at least caused the most damage, because she somehow had Archduke Ferninand assassinated and started the first World War, leading to the second World War, the Holocaust, and the Cold War. Pierre wished all French would be rude to Americans and Sammy wished that tornadoes would destroy trailers (because he hated them).
The three children then wanted to get revenge on their former godparents, but with the help of Cosmo and Wanda, Timmy was able to get them back in their frames. After putting the frames back on the wall, Timmy feared that he would be put in this hall due to trespassing on the castle and creating a lot of trouble in it. However his godparents assured him that it would not happen as they didn't want him to come into the castle until the Hall of Timmy was finished. No other godkids have been shown, and the room has not been shown since the episode "Hassle in the Castle".