Is it permissible to refrain from greeting some people with "Salam" due to shyness?

Initiating the greeting (salām) is a Sunnah according to the majority of scholars and not obligatory. However, it is preferable to greet every Muslim—whether known or unknown—due to the reward it entails and the strengthening of bonds. One should not allow shyness to be an impediment to performing righteous and praiseworthy deeds.