I want to stress: it is possible to get better, and achievable. You should do it early on, so that you avoid major problems.
Strategies that will help along the way (but of course, should be dropped as you progress):
-Earplugs. This helps.
-The biofeedback relaxation: a sign of you being tense is your hands get cold. If you think "my arms are loose, and warmth is flowing into my hands", then you can help warm up your hands. [You could pay a professional and learn how to do it like I did, but it is pretty expensive, and this was the main technique I learned]. Do this when in the bathroom. Also, try to relax your muscles. Go through each one: "my right hand is heavy. My right hand is heavy and loose. My right hand and arm are heavy. My right hand and arm are heavy and loose".
-Imagine you are in an outhouse in a forest with no one around, or some other place. In certain circumstances, imagine you are in a different bathroom, or are embedded in the wall behind you.
I want to stress--the bathroom really isn't a scary place. Those few years when I went out of my way to find handicapped bathrooms--eventually, I felt more awkward going to them, and some public bathrooms can even be rather private at times. It takes a while for your body to catch up to your mind, though; even your mind needs 8 weeks of cognitive behavioral therapy to avoid your associations with the bathroom. You probably need less time if it's early on.
Also--never give up hope. It will take a lot of time and effort, but it is the most important thing you could possibly spend your time on. You will be able to fix this, and parcopresis is curable.
You also need to tell someone who will support you along the way. For me, it was my mom. If it affects your relationships with other people, tell them. I told my roommate; it didn't help much because he was a pretty selfish person, but with a better roommate it would be worth a shot. Honestly, people are okay with it. If your friend told you they were afraid of going outside, then you would think it was a little odd, but you wouldn't not be friends with them, and I think you would support them. If you think your friends will make fun of you, you should find new friends.
One think I don't like so much about this site--it makes parcopresis almost seem acceptable, like it's a condition that you should resign to live with and join the club. [At least I kind of got that sense from reading a lot of the threads]. I want to stress: if you God forbid had cancer, you might join a people with cancer society, but the goal of the society isn't to accept your cancer and live with it; it's to beat it . You can beat this, it just takes effort.
I also can't stress this enough: if youa re in high school or college, you will probably have a counseling center that will provide the help you need for free. Take advantage! In my experience, the type of psychologist I got from teh counseling center was more helpful for family issues, etc., with not as much of a CBT bent, so try out a few different options. This is an important thing to do!
As for myself--I am still struggling a little. I don't think I am fully comfortable pooping if someone would watch me right in front of the stall walk in and poop. It isn't likely that peopel would do that, but going to school in Manhattan leads to some very public situations. I've learned to look at this as an opportunity, because in a few months, God-willing, this whole issue will be behind me, and I will be able to poop in the most public bathroom possible. [Still, I'm not sure if I'd be able ot poo in an outhouse in the middle of times square]. Right now, I am confused if I am constipated or not; I don't poop the way I used to, and the poop comes out in flat sheets. I hope my bodily functions will get back to normal. It is still hard to tell if I have parcopresis, because while I can go in public bathrooms, it is still easier in more private ones.