Happy You Left Dad Day!!! ????

My mom is the most complexed person I have ever met. To me, even more complexed than men! So, several years ago when I got a phone call (and trust me, she NEVER calls unless she wants something) from her, it left me with an even more complexed opinion.
Now, I cannot for the life of me remember what year this conversation took place. I want to say it was prior to 2002, but could very well have been after that but prior to 2005. Well, the conversation went like this:

Me: "Hello."
Mother: "Did you forget to call and tell me something?"
Me (after thinking for a bit): "No."
Mother: "Are you positive?"
Me (after thinking for a few more seconds): "Yeah I'm sure."
Mother: "Do you know what today is?"
Me: "Ummm.... January 6th?"
Mother: "Do you remember what happened X number of years ago?"
Me: "Ummmm...... No?"
Mother: "It was the day I left your dad!"
Me: "Ummmmm.... Ok......"
Mother: "You were supposed to call me and tell me Happy Anniversary!"

I mean seriously WTF? Why, after over at least 10 years, am I supposed to remember the exact day she left my dad?? It's not something I keep circled in red on my calendar. And what am I supposed to say? "Hey, Mom! Happy You Left Dad Day!"? And am I supposed to call my dad as well and say, "Hey Dad! Happy Mom Left You Day!"? What's the appropriate gift for this occasion? And does Hallmark have a line of cards for this? I mean she can't tell you when my birthday is, but she can tell you the exact day she left her husband!? And Nevermind the fact that my dad was remarried for at least 5 years prior to this conversation and my mom was in a relationship.

So, I quickly muttered "Happy Anniversary." and hung up the phone. I sat down trying to figure the whole conversation out. And honestly, I still am......