Leave him alone for Christ's sake. Isn't it lucky all of you are in jobs where any indiscretion isn't plastered over the gutter-press and NSC?
I'm not religious but there are some apposite lessons from the bible: "You hypocrite! First, remove the beam out of your own eye, and then you can see clearly to remove the speck out of your brother’s eye."
Getting your knob out, whist sat in your van, in front of a mother and her 16 yo daughter is a bit more than ‘indiscretion’ (as Moses said to Aaron - was apparently going to be the 11th commandment but he only wanted 10)