Firstly, Mr Gill, It saddens me to hear that you were put in such a position to start. No shortage of folk who's out there looking for trouble. Secondly, retreating from threats takw intuition so while I understand your sense of 'shame', if I were in your shoes i would have done the same thing for it was wise. As to how to overcome this, I am speaking from the perspective of one who competes in muay thai and has been taking self defense/street fighting classes for a few years. Becoming competent in some form of martial prowess is my recommendation. Not only does it bleed over into more aspects of your life such as the way you carry yourself (posture, speed of movement, facial signature) it will make you all the more formidable in the offchance some dipshit still want's to 'test you'.