Oh shit, oh shit,oh shit!

This is what I thought I heard from the back seat when driving to the shops yesterday.

Me:"Excuse me Alex? Did you say something?"
Alex: *pregnant pause* *giggle* "I laughed."
Me: "No, before that. I thought you were saying something to me?"
Alex: *giggle* "No."
Alex: "Oh shit- it's what you say when you don't know the song."
Me: "Really? Who do you know who says that?"
Alex: "No-one. Me."
Then I tried a little reverse psychology - to finally get a name.

Me: "That's not something we like to say - ok?"
Alex: "OK Mummy."

***
This morning -

Brett:"I got the 'Oh shit' this morning."
Me: "Oh..."

***
To think I've spent the past, goodness knows how long, biting back choice epithets...