My sister and I were walking down a busy sidewalk when I suddenly became aware that there were three boys walking right behind us, probably around 13 years old.
If you were ever bullied in school you will be very familir with this situation. It's basically a win-win for the bully, there's no good way to handle it while keeping your cool. You can keep walking and ignore them while they silently read your body language and know that they got to you. You can stop suddenly so they run into you, and they still know they managed to piss you off. You can spin around and whack them, or give them a piece of your mind, but no matter what you do the bully still wins.
The nice thing about growing up awkward is that you become intensely aware of all the details that make up good social skills. When you have to consciously learn the rules of social engagement, like how much eye contact to make and how close to stand to people, you learn a lot more than those who just acquire good social skills naturally. Also, when you really don't give a fuck, you can choose to disregard of those rules.
Invading someone's personal space from behind can make you feel powerful and intimidating. Face-to-face with a stranger, that same distance can be very uncomfortable. Prolonged eye contact with a stranger is even more unsettling. A stranger walking backwards for the next two blocks while making direct eye contact and grinning can be very uncomfortable. Yes, junior high boys, you may be annoying but I am crazy.