Check out this Pennsylvania Coalition Against Rape's PSA video.
I need to mention that the man's or boy's actions are no less deliberate if he doesn't add anything to the alcohol he urges her to drink. If she's incapacitated for any reason, and at anyone's hands, you have a moral duty to make sure nobody uses her. Walking away and leaving someone vulerable to another man's desire to rape isn't proof that you are doing the right thing by not raping her yourself. Just because you haven't committed a crime doesn't mean that your hands are clean.
Girls who try to prevent rape by taking precautions and watching out for other girls don't have it easy and boys and men need to accept that taking the needed action to prevent rape won't always be easy for them.
If you snear at girls and women who are afraid to speak up during an attempted rape, but refuse to speak up or call 911 when you see a bad situation in the making or a possible sexual assault, you need to realize that you are being controlled by fear or by cowardice or something ugly inside yourself and are no better than those you snear at.
If she didn't want to do it at that time or in that way and cannot easily walk away, it's rape.
If she started the interaction willingly and in full capacity and loses motor control or coherency, stop. To continue is to cross the line from mutuality to rape.
If anyone besides her gives you the okay, no matter how trustworthy they seem or how convincing their explanation, it's rape.