If you put on a ski mask and go into a bank with a fake gun, or a banana for that matter, and yell that it's a robbery, or even yell that it's a fruit delivery while waving your banana around... you don't get to excuse that shit with "it's just a prank bro". It doesn't matter if it's a prank, it doesn't matter if he's trolling.

He broke the social contract by being a cunt, and the only reward he gets for his trolling/prank/insane rant threatening bodily harm should be a significant amount of clicks on that little "report" link under any comments he makes that are against the rules of the subreddit, reddit's sitewide rules, or general rediquette.

Do note that rediquette discourages trolling and insults, while reddit's sitewide rules outright forbids all encouragement or incitement of violence as well as threats and harassement. Comments like this are quite clearly something the moderators and admins want to be made aware of so they can judge for themselves whether the poster has crossed a line or not.