Eye raping is a slang term for the act of staring at someone in an unwanted sexual fashion. The term uses the word 'rape' because this type of staring is seen as a violation, even though it is not a physical attack.
Similar to 'eye raping' is 'eye fucking,' a term that hit the mainstream after the film Wedding Crashers. Whereas eye fucking is more often a consensual act, the term eye raping implies that the sexual gaze is unwanted by the person who is being watched.