Gangrenous penis is where a male's penis is restricted from having blood flow for so long that it dies, causing the tissue to rot while attached to the body.
You: Why does my dick look like that?
Doctor: Because you have Gangrenous Penis.
When your penis has been insulted so much by, lovers, potential lovers, other males/students/peers, that what little blood you already had flowing into it now stops, cutting off your circulation and causing your penis to, blacken, shrivel, dry up, and then promptly fall off. This then spreads to other parts of the body until death but, you are writhing in SO much pain from your overly circumcised chumpy chode, that you don't even notice it.
Person #1:"Fuck man! I got Penis Gangrene!"
Person #2: "GET THE FUCK AWAY FROM ME FAGGOT!"