Sorry for Blowing Up
A brief, but sincere apology for blowing up at a person.
I feel terrible about my behavior on [Date]. It's been bothering me a lot and I just had to send you a note of apology. There was no reason for me to blow up at you like that, [Name]. It was uncalled-for and hurtful and I have no excuse for what I did.
I am genuinely sorry for how I acted. Will you please forgive me?