My female friend and I disagree on whether a male can be raped by a female. I say yes, she says no. I say that erections are not necessarily caused by arousal. They can be caused by other things such as anxiety. Get ready to say I told you so because you are right and your friend is wrong.
Men can, and are, raped by women.
Though there are many backwards ass states in which a woman can not be convicted of raping a man due to how rape is defined in that state. Usually she is charged with sexual battery, if she is ever charged with anything at all. This is related, in part, to two misconceptions. The first, that men always want sex and women don't have to force themselves. The second that men must be aroused to have an erection.