Welcome! Hope you stay and continue to contribute well written posts like the above. You've obviously won over some of the most valuable pundits here. For example:
I'd go one step further, and send a PM to Admin asking him to delete all your references to poisoning your coworker, as well as references to it in others' posts. Why? Because you've also disclosed the identity of your workplace, where, through no evident fault of your own, you already seem to have an enemy. Your description suggests the problem will not disappear and may intensify.
Venting publicly about identifiable opponents invites retaliation, and you've made it easy for someone to frame you for a crime you joked about, with permanent consequences. We don't want you to have to be telling a jury "But it was a joke! I would never do that!" after your pal at work, or one of his pals, actually does spike his coffee and then points to you.
Whether or not you take my advice, again, Welcome, and do realize that everything you write on this board and in the places to which your writing here links may be read and used against you. It's happened before. And we'd prefer to see you achieve the goals you wrote about so nicely!