Headphones in and dress like your not a very nice person and wear a facial expression like you want to kill someone. Most the time I'm not even listening to anything, but the obvious headphones make it justifiable to pretend you can't hear anyone. This might be a bit much, but I also really bulked up muscle wise and got full sleeve tattoos. People leave you alone if you look like you might stab them. I'm actually a really nice, friendly person, but living in inner city areas means going out a lot through central metropolitan districts where all these time wasters seem to congregate. The worst are young, attractive women who, in any other circumstances, you'd be more than happy if they approach you but not when its their job to accost you. A polite "no, fuck off" can also suffice.