Also, even if it fit and was a clean cut, the human brain retains conciousness at least 70 seconds after being severed...Don't think that would work in America, I spent a week in Houston back in 2017 and I dont think anyone's neck would fit through that hole.
The cleanest way to go is nitrogen inhalation...
For super rich dudes like Gates, Musk etc it would be by standing within arms length of a nuke denotation the radiation would vaporize their cells in under 100 nanoseconds, faster than pain signals can even reach the brain