Your name says under 18, so I would assume you go to high school? Do they allow yoga pants at yours? I know some places don't as they prohibit 'tight' clothing. If you're in college its a moot point, I knew plenty of people who just rolled out of bed in pajamas and showed up. You would have to put effort into looking stupid there.
welll I've worn black yoga pants and black tshirts to gym and i got no dirty looks. this is with people i dont know too so it should be fine with a bunch of people you cool with. I've also worn black boots, jeans, and jacket, bf approved :|