Bart Simpson and his sister Lisa.
Now, close your eyes and form the following image in your mind. Bart has unzipped his blue shorts and pulled out his pecker. His adorable wide-eyed sister has leaned down in front of him and started to give her brother a tender Olympian blowey... as they say in the sporting classics. Specialists (elsewhere on the Internet) have suggested that this incongruous composite image might look something like this: