It has been said a few times, but with all joking aside I have to agree with what the majority has stated.

I would eat the deductible, get it fixed but deffinitly speak to him about it. Just explain that you heard him bang into your car the other day, and that it caused a bit of damage. Just to ensure he knows this transpired and hopefully will be more careful going forward. Don't elaborate on the damage or cost, if he asks tell him your insurance covered it (which is a mostly true statement). If he really presses you on cost and wants to reimburse you, let him but otherwise chalk it up to a life lesson for everyone and go enjoy your car!