Dear {Recipient},
I'm so sorry I {action}. I can see now that {action} was just too much for you to handle. Even though we've been friends for {number} years, one little {action} is apparently too much strain on our relationship.
After all, it's not like I put up with you when you {past action}. And it's not like you ever {behavior}. So please, forgive the monstrous way I behaved. I know that you are perfect, so clearly you must be right about this (like you always are).
I'm happy to bow down to you and grovel at your feet. After all, {action} was a misdeed on par with clubbing a baby seal. So, please feel free to continue to ignore me like the scum of the earth I am.
With the utmost regret,
{Sender}
