In America, rape doesn't necessarily have to involve either a penis or actual force. Since the Constitution doesn't cover the subject, it's left up to each individual state to give a legal definition to the word.

There is no national rape law in the United States. Each state has its own laws concerning sexual aggression. Nor is there any national standard in the US for defining and reporting male-male or female-perpetrated rapes. More than half the states use traditional sex-specific rape law, limited to male perpetration against females.[citation needed]
In many states, a female who is younger than a certain age is unable to give consent. Sexual activity in this situation is therefore automatically considered to be rape.

You begin to see the problem?