Now that I have kids I look back on some of the things I said to my parents and it nearly breaks my heart. Typical teen things like "mom, you're so embarrassing" or "please don't sit BY us in the movie". Im certain that stung and I dread the day when my kids say them to me. As my mom always said "Just wait till you have kids!"
There is also the big things that I took for granted growing up. The expensive clothes or the spending money, as a kid you just dont know how hard it really is to be able to afford just living, let alone extras. My parents were/are hard workers.
I also never understood why my parents divorced. Cant you just get along and love each other? Marriage is hard, raising a family is hard, I get now that my parents did the right thing for everyone involved. They made a clean separation, never talked shit about each other. They are both remarried and happy, they can hang out with each other and their spouses for parties, weddings, no awkwardness or drama. It's really the best thing I could have ever hoped for.