Did you make a fool of yourself at Mom's house again? Say you're sorry with this letter, because you never call, do you?
1234, Main Street
Boston, MA 02123
07 April, 2005
<Recipient Address Goes Here>
I wanted to write to tell you how embarrassed and sorry I am for my behavior the other <day/night>. It was unforgivable of me to <description>, especially in front of my family. I wish I had a good excuse for what I did, but some things we just have to chalk up to stupidity and insensitivity. I really don't know what came over me.
I offer this apology from the deepest place in my heart and hope that you can bring yourself to forgive me for being so rude. I will do everything in my power to see that it never happens again.
encl: <List of enclosed items goes here>