In a recent magazine interview, Mila Kunis admitted to being a difficult teenager in the past, and she even apologised to her mom when she was 21.
Let's face it. Most of us were difficult in some way as teenagers (or even when a bit older), and we probably do owe our parents an apology.
I think we should make this a popular thing to do. Take your mom (or dad) out to dinner, and make the apology sincere. And tell them how much you actually appreciate them, now that you are older.