Your employer would also be at fault for not forcing you to wear proper PPE. Stupid world we live in.
If you sign a daily safety/toolbox/pre job hazard assessment/field level risk assessment paper, that releases the employer from any and all incidents where your neglect put you in harms way.
My ear muffs are sacred. I'd consider myself a new shooter as well (got my PAL last January) and I learned the hard way about hearing protection when I fired the first round from my new SKS (I had forgotten my muffs) and went temporarily deaf. Now I always tell people to wear them and hand them out, warning of what can happen to their ears. If they still refuse, they've lost the right to complain about losing their hearing. It was their own choice.
You didn't muzzle blast anyone. Your friend didn't want to admit he was being stupid and shifted the blame. Don't feel bad.
For some people, learning the hard way is the only way to learn.
Happened to me today. Firing a savage 308. I HAD hearing protection on but the rifle seemed so quiet I tried without. Huge mistake. My ears are still ringing from the shot 9 hours ago. I was in physical pain. Felt like someone punched my inside my ear. That's not even possible. God damn.
From someone who has constant ringing in their ears, NEVER shoot without GOOD hearing protection. Don't cheap out on your ears.
You should have shot them. You can't fix stupid but a bullet wound would be a good learning aid.