A hard-on so fierce that it not only peels the skin away from one's face, but also drains the blood from rest of the body and threatens to kill the host.
An erection of such magnitude that it stretches out all the skin in your body, leaving even the skin on your face so drawn and tight that all you can do is utter "help me," which, because of the taut facial skin, sounds like "reltney."
A raltney is a hard-on so intense, it uses up all the excess skin in your body and you are no longer able to blink your eyes. It is worth it. All you women out there, I am sorry -- I cannot vouch for what it will do to you. I hope it is as enjoyable.