The Mystery Of The Offended Bagger Boy

Today I went to Felpausch for groceries. I got cat food, shower gel, AAA batteries for my camera, bath powder, a bottle of water, and a bottle of Excedrin. While I was waiting for the cashier to ring it all up, the bagger-boy said "Everything going ok for you today?"
It was an unusual twist to the usual meaningless monotone of "hello-how-are-you-today."
I joked, "Oh, y'know, it's the weekend; that's all I really care about!" I waited for him to smile back, but instead he got totally silent and looked kind of offended, as if I'd just told him to take a flying leap onto a vertical popsicle. And then he left to go bag someone else's groceries instead.
"What happened??" I wanted to shout. "What did I say?"
But instead I just paid for my stuff and left, cursed with the "mystery-of-the-offended-bagger-boy" for the rest of my natural life.