A person’s personal space is the comfortable distance from another person, with strangers as a usual reference. It is the ‘safe’ space around them with which they feel comfortable. Different societies have different norms on personal space. With some societies, individuals get extremely close to another, and this may be jarring for those who do not share the same views.
Invading someone’s personal space can make them feel uncomfortable at best, and threatened at worst. Doing so can have a variety of unwanted outcomes. There may be mentally unstable individuals who may lash out physically, and you would never know. Because of this, it is best not to invade the personal space of someone you do not know well.