Same problem here! You don't care about your girl you cheat you put your d*ck above everything etc... Have heard it a lot even from friends who after a while of knowing me better talked to me and said everything they've heard for me! I've even heard that I have bitten a girl LOL! Many of them are true, just like in you I guess cause no romours come out of nowhere, but you either can prove them wrong or even accept what will make you a greater catch!
A good way for using this bad reputation is: "If you think I am that guy maybe you should get to know me better and see for yourself what I am all about"
Advertisment is good even if it's something bad! In my college a teacher told us that there was one guy who had written a book about how bad the advertisments are! The book didn't sell at all so he came to the point that he had to, and advertised it on tv!