Sacred cows roasted here

As I walk into the bathroom the other night, I see the wife viciously flicking her tongue with my toothbrush.
Wife: "Oh, here. Sorry I used your toothbrush by accident."
I was speechless. She then laughs, because the look on my face is priceless she says. I understand about germs and kissing and all that, but it's the principle. Is nothing sacred?