Xbox Live, report the gamertag with a description. Or send a message with your screenshot to some TC member or a mod to forward it to TC. Either of those should result in some form of action.
That said, forum rules technically don’t allow public calling out so I don’t think this was the best place to post this.
Edit : I do think it’s funny and sad at the same time that someone gets so upset over a damn video game that they wish someone death. Mostly sad though.
For In-game text
File under “report”