The other night as we were playing with our new Wii, Girl let the f-word fly. She had lost to Boy again, in her favorite Wii sport, bowling.

We had banned her from Wii boxing because after a loss there, she started flinging the nunchucks at Boy, fists pumping, turning the virtual into reality. She does not lose gracefully, especially not to her smug older brother.

Boy and I just looked at each other in shock when we heard Girl spew out the f-word, and I bit the insides of my cheeks so as not to laugh. Yes, I am a bad mother — I thought it was funny. But I am not such a bad mother that I let her know I thought it was funny.

“Ooooooh, you said a really bad word,” Boy said.

“Yes, that’s a really bad word,” I agreed.

That sent her crying into the other room. How could I convey the severity of the word without explaining its meaning?

“If you were at school and said that word, you would be sent to the principal’s office,” I told Girl. “And you’d have to flip your card to red,” the worst conduct grade there is, an unimaginable consequence for Girl, who’s been on green every day of kindergarten so far.

In “A Christmas Story,” which we just watched, Ralphie is punished with a bar of Lifebuoy soap in his mouth for saying the f-word. I don’t think I could even squirt a little body wash on Girl’s tongue — it seems a tad Medieval to me.

Like Ralphie, I’m sure Girl picked up that word from home, even though we try hard not to swear in front of the kids. But apparently, not hard enough. The thing is, she said the f-word just like I do, accentuating the hard “k” at the end. And for the same reason — when you want to punch someone in the face, but can’t.