I rose my hand.
"Yes, Mike?" she called on me.
"It means my sister's birthday is today, and I forgot to get her a present."
The class laughed, the teacher arched an eyebrow at me, and I amended my answer, "It is also the day when Brutus betrayed Julius Caesar and assassinated him."
So Happy Birthday, sis. I still didn't get you anything, but that'll be after I take Dad to dialysis.