Apology Letter For Joking Around
Dear {Recipient},
Please accept my apologies for joking around at {event}. You were right. That was definitely not the time and place to be cracking jokes. I'm sorry I acted like a fool.
Rest assured I have learned my lesson and you can expect me to display proper behavior in future such events. I promise to not {disappoint/embarrass} you again.
Sincerely,
{Your Name}