Regardless of how old you are there will always be bullies and predators out there looking to harass you. The trick to keeping people from bothering you is to make it seem like there's something mentally off about you. Bullies will only take on people who they believe will not retaliate against them. Some people think merely acting tough is a good way to keep people from bothering you, but that's not always true. For instance if you walk into a bar and tell people not to mess with you because you're a "Tough cookie" this will usually only make people bother you more, trust me.
The trick is in making yourself seem mentally
unstable, NOT mentally handicapped. That's an important distinction to
make. What I usually like to do is if I'm walking through a strange
neighborhood I will throw in a twitch every now and then. Don't make it
too obvious because that will only draw attention to yourself from far
away and invite trouble, but just twitch weirdly maybe once every
fifteen seconds. Also clench and unclench your fists and mutter to
yourself incoherently. This sends the message that you're deranged and
ready for violence. Another thing you can do is punch yourself in the
face. I would advise against slapping yourself in the face because this
tends to just look stupid and the sound draws unnecessary attention, but
punching makes you seem crazy. People will see this as a sign that you
don't fear pain and immediately back off.
The last thing I like
to do is usually chew gum save up all the saliva in my mouth. This way
you're walking around with big puffed up cheeks, which is an
evolutionary tactic for many animals to scare off potential enemies.
Also, you're seen as mentally unstable and a wildcard. No one wants to
mess with someone who's walking around with puffed up cheeks. And the
third way this works is people will know it's saliva, but they don't
know where you've been so you could have any multitude of viruses and
diseases that are transferable via saliva and if you've got two cheeks
full of sickness juice people are going to take note and not bother you.
Best thing is, even if they do you can spit in their eyes like a
Dilophosaurus from "Jurassic Park" and then either use that as a
diversion tactic to run away, or get in the first strike.