4x23 - 3rd Rock from the Sun

The Big Giant Head sends a message that he intends to visit Earth, so Dick quickly orders Sally to move back in and Harry to stop attempting to make a baby with Vicki. He then attempts to prepare Mary for his visit by telling her that an 'old college chum' is visiting and that she would be well advised to discuss how much he has learned in bed. Harry tries his best to avoid Vicki, but eventually resorts to telling her that he can't father a child with her right now. When the Big Giant Head arrives on Earth, he is unimpressed with Dick, his leadership skills and his choice of girlfriend, while being impressed with Sally, her style, and her body.