An asshole thing you do in order to save your own ass. It's considered saving your dick when you screw someone over really bad just to getout of something yourself making it 10 times as worse as just saving your ass. Once someone has "done it to save my dick" they have caused a never ending cycle of people fucking up other people just to save themselves. The only way to stop this cycle is if someone manages to get to the person who started it all and either narc on them or beat the shit out of them. If someone screws you over and says they did it to save their dick, they are completed justified and you have to deal with it or fuck them up.
Friend #1: Dude, why did you tell your mom that I was the one who pissed on your couch?
Friend #2: Do you know what would happen if my mom found out I did it? I did it to save my dick.