My child threw an empty milkshake cup out of the car window! In fact, I'm not even 100% sure he didn't smack a car with it. I just caught the cup flying out the window through my peripheral vision.
You. Have. Got. To. Be. Kidding. Me.
At that point I knew, reasoning was out of the question. I just went with how incredibly naughty it was to litter, and to never ever do it again.
My kid threw his McDonald's happy meal toy out of the sunroof because it was "stupid".
My son yells from the back seat, "My feet are hot" then took off his shoes and socks, rolled down his own window, then threw his socks out.
With the exception of my kid possibly smacking a car with a milkshake, I wasn't feeling like such failure after hearing my girlfriend's horror stories.
The only bright light in all of this was realizing that all those children's shoes, toys and clothes on the side of the road are not the result of foul play, but rather, foul behavior!