it would be quicker
Quicker..?
How could it be quicker than any of these things?
Body bag: Body bag them, done, good idea to hide them though.
Melee weapon: Pick them up, set them down, hit them in the back, done.
Medicine trick: Since a player can only go unconscious once (taser does not affect, and is not affected by this limit), using the medicine to revive them and potentially kill them immediately after is just as easy as hitting someone in the back.
Your rope idea: You can't just tie a rope around their neck, they would have to be hung from somewhere. Either this would take ages to code, or be stupidly hard to use. And to top that all off no one's going to use it except for that one laugh and then they carry on with their lives.