Frank's younger brother, Uncle Joe has a sibling rivalry with him. When Manny started potty training, Uncle Joe insisted that there was a "potty monster" about to get him, causing Manny to fear using the bathroom for a couple years, so that meant Frank had to change his diapers for a longer time. Also, Uncle Joe's children call Dad (Frank) "Aunt Fwank [Frank]", which Frank swears he told them to do on purpose, but Susan thinks it's cute. In book 4 Greg mentions that he tried to make Uncle Joe to convince Frank to get a dog. He also mentions that his dog, Killer ate some of Greg's birthday cake.