Given the following context:  The crew of a malfunctioning alien cargo ship make an emergency landing on Earth. This draws the attention of four sexually-frustrated humans in a nearby park: Oliver and Prudence (a mild-mannered professional and his highly-strung fiancée), Willy (a bumbling shop assistant) and Cliff (a middle-aged man). Oliver, Prudence, Willy and Cliff wander into the ship and encounter three aliens resembling human women: engineer Partha, nurse Cosia and the captain, known only as Skipper. Willy inadvertently drops some pornographic magazines that he has recently bought. The aliens mistake some approaching cows for a hostile force and hurriedly take off, despite warnings from the long-suffering computer about the precarious state of the ship's systems. Resuming their original course, they study their guests in detail. Fascinated by the anatomy of the males, they decide to sell them to a zoo for exotic lifeforms on a distant planet. They also debate the significance of the acts depicted in Willy's magazines. Partha is particularly keen to emulate them and enthusiastically has sex with Cliff. Skipper, Cosia and Partha subject the males to a series of tests to learn more about their abilities. Oliver and Cliff fail miserably. However, Willy, looking for his magazines, beats Skipper's combat simulation by unknowingly evading her attacks, causing her to collapse with exhaustion and infer that he is a stronger being. While conducting a physical examination on Willy, Cosia discovers that his biology is more advanced than anything known to their species; encouraging Cosia with exaggerated claims about his sexual prowess, Willy loses his virginity to her. Later, he passes an intelligence test by a fluke and has sex with Partha.  answer the following question:  Who are the men that fail the tests of the aliens?
Cliff