Since Benny didn't have an opposite-sex parent, the wish sticky created one for him, so that the wish could still be fulfilled.
Suddenly, Benny's pants seemed more loose than normal. He put his hand between his legs and nearly screamed when he realized that his penis was gone! There was no bulge. There was nothing.
He shut the front door, turned around and got another shock. Sitting in his kitchen was a woman. A woman with a bulge under her skirt.