He's Just a Bit Tired

J and I are at the checkout of our local supermarket where the cashier attempts to make J smile.

Cashier: Hello!.. Hello!...

A small amount of gurning later...

Cashier: He's not up for smiling today, is he?
Me: He's just a bit tired.

For reference, this is always a good stock-in-trade answer. She tries again, waving her hands. 

Cashier: Hello!... Hello!...

I attempt to help things along by coaxing his cheek. He maintains a steely gaze.

Me: Go on, give the lady a smile.
CW: Ah well. That'll be £18.24 please. 

I pay for the groceries. An old man squeezes past with his own bags.

Man: Hello little fella!

In full view of the cashier.J breaks out into the biggest grin I've seen in ages, complete with full arm and leg waving.

Man: Lovely.

Pause

Man: Do it again.

J obliges with another bout of smiling and waving.

Man: Do you know what? That has really made my day.

The man walks off smiling to himself.

Me: (moving away, not looking at the cashier) Has someone decided to wake himself up?

I find these little explanatory phrases fascinating. We're always using them to indirectly explain an action or justify a situation.