The ramifications physically of bad posture affect you regardless of any of this. If you really want to cur out the outside world more while walking, wear a brimmed hat low on your face but keep your head up.
Heh, yeah. But you don't have to pop your veins out of your neck. And if you have a skip in your step and/or wear some quirky colorful clothing, people won't see you as aggressive just for having good posture and a low hat.