Re: most violent episodes (& TV Parental Guidelines rating system)
The climax of Terra Prime, when a crewman who sympathises with the xenophobic movement commits suicide in front of Archer. Not sure the mess a phase pistol would create to the guy's head, but presumably more horrific than Valeris' close range stun of Burke and Samno in Star Trek VI.
But we didn't see that, did we?
"I'm creating a (free) universe, just a hobby, won't be big and professional..."