"Did you know I've been looking for you since the 7th grade?""
Bobo the Rabbit is the rabbit that Heinz Doofenshmirtz used in his magic act when he was in 7th grade.
During a 7th grade magic act called "The Improbable Doofini", Doofenshmirtz tried to pull Bobo out of his hat, but instead accidentally pulled out a skunk. After that event, Heinz looked for Bobo until his adulthood, wherein he found him with the help of Perry the Platypus when he tried to perform magic again. Perry had made Bobo appear when he shot him out of Heinz's hat. Heinz then remarked, "Bobo the rabbit, did you know I've been looking for you since the 7th grade?" Perry then proceeded to shoot hundreds of identical rabbits out of the hat. The combined weight of all those rabbits brought the hot air balloon falling out of the sky, right in front of the Farmer and Farmer's Wife. It is unknown if Bobo the Rabbit was sold with the rest of the bunny farm, or if he remained with Doofenshmirtz. ("Leave the Busting to Us!")