This is autobiographical.  My stepdaughter pulled this trick on me when she was a kid.
She rolled the passenger window down, inserted broken bottle shards in the rubber of the car window, and left a skateboard and glass shards in the passenger seat.  Glass shards on the garage floor as well.
I freaked out that someone smashed the window with a skateboard. It looked totally real.
Of course, in this comic, Luna actually DOES smash the window.
I showed Luna this strip and she was shocked by it.
“I would never do that!” 
John Vogel