Well...
To put it bluntly, I regret that, a few months ago, I thought God hated me because I thought it was unfair and done on purpose that other people got to have such great families and everything went right for them but not for me. It wasn't the happiest time of my life.
I also regret this one time I gave my best friend the cold shoulder for no reason except that I thought he didn't care for me as much as I did for him.
Otherwise, there aren't a lot of things I regret. Maybe at the time I did, but not now. Everything worked out all right.