Kind of a regret. I really wish I had gotten into martial arts like I am now alot sooner. That and taken better care of the body when I was younger and been into fitness and staying in shape during my growth years. Now I am not by any means in bad shape, but I sure as hell could be in better condition. Wish by all that is holy I had never set one foot inside a Community College, although strangely enough had I not I might never have sparked said interest in martial arts. I also regret wasting time applying for scholarships I had no chance at and all the effort trying to go to a school I was never going to be able to afford.
Girls! Oh good lord I screwed up every time! I wish like no other I would have just once got it right, not been so stupid, asked the right girl, not assumed just because she was good looking she was already taken, asked that girl out when I had a chance etc. (Sorry that was so long.) That or have always been like I am now and had zero interest in relationships. Strangely, I regret always getting good grades, as it didn't really make me friends or even help me get scholarships, just create unnecessarily high expecations.
I ended up really regreting having ever taking part in Ampgard, thanks in large part to an arsehole who is supposed to be my friend putting on a winch wig and hitting on me, and he just wouldn't stop no matter how much I asked him. It was exacerbated by everyone thinking it was just innocent roleplay.
But now I have my aformentioned martial arts, so it is all good. (mostly)
Sometimes though, I do wonder how things would be different if I had been an idiot, a jock, a skaterguy, or some combination thereof, or really anything other than a nerd.