I wonder what's holding you back, too. Well.. like Triangle said, it's obvious that you want to do it, but I'm just considering what's keeping you from doing that.
Are you afraid of how you'll be viewed if you end up getting a boner in school while freeballing in sweat pants?
Do you have some kind of guilty conscience about exposing the shape and size of your dick while freeballing in them?
Maybe you're not satisfied with your total appearance? It seemed really hot when the good looking guys and buff jocks (in high school and college) would wear tight jeans or cut-off t-shirts that showed their navels and polished abs or sleeveless shirts where you could see their nipples sometimes when they turned or their underarm hairs. Those emblems of masculinity shown so boastfully are forgiven by girls and guys alike when the guy doing it is popular (which usually means he's rich, good looking or talented in sports or something else or can make people laugh or garner support by making fun or otherwise influencing others).
So maybe you need to work on your image. I'm not saying your self-image needs work.. it's up to you to decide that. But maybe you should try a make-over. That is try out a significant change in your looks, attitude, fashion or behavior and see what effect it has on people. It will likely also have a pretty big effect on you, too, once you see how people react to and notice you differently.
As an example, I sometimes try an experiment at my school. Being a college professor I can pretty much dress as I like: jeans and t-shirt, three-piece suit, ethnic attire (kilt or Japanese yukata), or just casual khaki pants, shirt and jacket. Of course, I'm (mostly) freeballing in any and all of these. However, it can notice a difference from the very fact that I dress differently -- even though no one may draw attention to the fact that they even notice the change. People's eyes move to places and parts of me that I hadn't noticed them doing so before, or people who normally don't greet me will, all of a sudden, say 'Good morning.' and even start casual conversations.
So you should try it out first -- without freeballing as an issue -- first of all. Find out how much you do or don't like the extra attention. If you find you like it, then your own self-image will change, and consequently, so will your confidence to freeball (or not), and to be your own person.
Of course, good hygiene, clearing up skin acne, a nice haircut and a little styling, trimming down or buffing up the body using by getting a good diet of the big 5 and regular exercise, as well as a little muscle and stamina training will also do wonders.
Finally, I suggest you try my long standard 'wardrobe fix'. Here's the way it works:
Wear open front boxers under your sweats, but then pull your cock and balls through the open fly in the boxers and pull them up. You'll feel a little constriction which might make your cock swell up and fill out. But if you do pop a boner or drip after a piss or leak precum, you'll have some 'protection' to cover up with -- just in case. Beside, the lift it gives you dicks and balls looks and feels great.
If you're going to freeball, you might as well to it in sweats, then everybody ought to get the benefit (so let them see that you don't care about whether guys or girls (or horny teachers -- like me) see your junk.
If you really can't because it'll just be obscene, then gradually work your way up to that by trying the technique above or my wearing different styles of pants, trousers, jeans, dress pants (suit), athletic gear, hiking pants, etc...until you start to feel free, comfortable and not afraid to show off what Mother Nature (and your DNA) intended you to possess.
Go for it, dude.
I will repost on my personal blog, I plan improve my written response, adding more photos, so you can see it on: http://profile.typepad.com/sunbuns