"No way you can have a daughter that old! You look sooooo young. You must've been 12 when you started having kids!"
But it turns out she got pregnant in high school and so you weren't that far off?
I'm not saying this happened to me (recently)... I'm just saying I say crap like this all the time.
If I had a camera with me right now, I would take a picture of myself in a yoga pose sticking my foot in my mouth.