Personal space is important. It is defined as "the region surrounding a person which they regard as psychologically theirs." And for most people, there are about four layers of personal space to abide by; intimate, personal, social, and public. If a stranger came into our personal sapce, you would feel discomfort but if you're best friend came up and gave you a hug you would welcome it. We all have personal space, but it's how much or how little we have that spurs how we react.
Intimate and personal space is reserved to those that you have known for a long time and feel comfortable around. I observed that when interacting with people you are close to, you ave no problem getting into their space, standing close to them, or even touching them.
Social and public space is reserved for when you're, well, out in public. When you're shopping or running errands or at school or the movies, you have to remain a certain distance away from people. I would say about 12-18 inches would be appropriate, but the only way to know is to stay far enough away that you're comfortable and so you don't see any noticable discomfort in the other.
One thing the rules of personal space don't apply to is crowds. When you're in a large crowd or even a small crowded space, you have no option other than to stand too close to strangers. Crowd or no crowd, nobody likes a space invader. One way that we deal with this is by not making eye contact, not interacting with them, and basically pretending the person doesn't exist. For example, in an elevator, everybody faces the front and doesn't talk or look at each other. If the person next to you were to turn to you, you would feel a little awkward and they don't even have to say anything to you.
And interestingly enough, culture plays a huge role in our personal space and how we react. In countries with large populations, personal space is something you don't rarely encounter. When I was at Ikea with my dad one day, we were getting some lunch (and if you've never had lunch at Ikea you should know that it's kind of like a cafeteria where you get your tray and food and then follow the line). The lady in front of me, who was oriental, kept reaching back to get things (napkins, sauces, to refill her drink that she spilled) and she had no problem reaching over me and right in front of my face to get them. She wasn't being rude or mean, but she was invading my personal space and didn't seem to notice. I mentioned it to my dad when we sat down and he told me that she didn't realize she was encroaching on my space because personal space boundries are a lot different in Asia where there are a lot more people in a lot less space. I didn't harbor any negative feelings for the women, but I wished she could have altered her boundries a little to respect mine.
Getting back to the point, a person's space boundries depends on who they're interacting with, where they are, and how they define personal space. There are so many factors that go into it, there is no way to just know how someone is going to feel about you getting "all up in their grill." So don't be a space invader, respect peoples' personal space!
