WHAT "birthday lunch" ?

My 14 year old son and I went to dinner with my parents at a fabulous Italian restaurant that I used to frequent quite often. 

Both my parents and I commented that it had been a long time since we had been there.

     "At least a year," said my dad. 

My 14 year old (with the younger, fresher memory) disagreed.

  "You, me, and Grandma were here for lunch for Grandma's birthday," he said. 

My mom's birthday was in March, which would have been 6 months ago. 

  "We were?" my mom and I both asked, simultaneously.

My son looked at us like we were crazy.

     "I'm sure he's right, " said my mom, laughing.

     "Oh, I'm not doubting it, " I said, " But I got NOTHIN.  NO recollection."

My mom and I stared at each other, blankly, as we both tried to will the memory upon us.     

March.  Dolce Vita.  Lunch.  Birthday. 

     "NOPE!  Nothin," I surrendered.

My mom and I just laughed, as my dad sat confused, and my son just looked at us like there was something terribly wrong. 

My question is, "My parents, though still quite sharp (they will appreciate that), are in their  70's, but what's MY excuse ?"

I think I'll blame it on parenthood, and have another sip of wine.   

So, even though my SON remembers, it's HIS fault that I CAN'T !  ; )