Well, I can't say I blame you.
What he did was stupid, and, I would've told him so in no uncertain terms.
Trigger or muzzle control, simple mistakes can be corrected by firm, but,
semi-pleasant language, but, what he did was wrong on many different levels.
#1- Unsafe. Completely. Catastophicly unsafe.
#2- Lack of respect for your property. Just on the respect issue alone, I'd tell him to take a hike.
I'd consider taking him back if he asks you, but, you need to have a serious, no BS
discussion on what will be, and, won't be tolerated.
Make it clear, in no uncertain terms, one violation, and, he can take a hike for good.
You used strong language, but, I think that's the only thing you could've done at the time.
Don't worry.
I shoot alone most of the time.
But then again, I don't like people.