Congratulations! You've set your sights on a lofty goal, being one of the worst public speakers imaginable. It will take a while and require a lot of practice, but if you do your best at being the worst, soon nobody will want to hear you speak in public. Follow these simple rules, and you'll soon develop a reputation as one of the worst public speakers around!
1) Mumble and Speak Softly: Good public speakers want their messages to be clear and precise, easy for listeners to follow, so in order to be the worst you need to be as incomprehensible as possible. Mumble when you talk and speak softly, so that none of your listeners can hear what you say or understand your words. If even the front row of your listeners has to lean in to hear you, you're doing a great job.
2) Avoid Eye Contact: The last thing you want to do is look at the audience; they might mistakenly understand something you've said, or at least think that you genuinely want to connect with them. Instead, look almost every place else; the ceiling, your shoes, the walls, or behind you, away from the audience (perfect if you have a chalkboard or white board to stare at the whole time). As long as you are looking somewhere other than towards the audience, they'll get the clue that you're really not interested in them.
3) Move Constantly While Speaking: Whether it's a simple nervous twitch or full blown pacing up and down the stage or other public speaking area, you want to make sure that you never stop moving. Not simply walking calmly or making a few hand gestures either; you want to be moving frantically and unpredictably, one minute circling the stage, the next minute waving your arms around randomly. At no point do you want your movements to have anything to do with what you are talking about; the less sense your actions make, the better.
4) Don't Practice Beforehand: The very first time you say your speech should be when you are on stage, looking at an eager audience who expect you to talk like a professional. Even if you are an expert on the speech material (and why would you give a speech on something you know when you're trying to give a bad speech?), if you don't practice what you want to say, you'll be sure to struggle with the speech, making long pauses as you try to find the words you're seeking, and fill the speech with ums and ahs.
5) Don't Write Down Your Speech: While we're on the subject, you definitely don't want to write down your speech or any notes about what you want to say. If you have notes, you might stay on track with your speech, covering the material you wanted to cover, and generally staying on track. If you do keep papers on you during your speech (perfect for if you need something to look at rather than your audience), make them random and unorganized, flip through them at regular intervals, and read the most boring and irrelevant parts throughout your speech.
There you go; if you want to be a horrible, atrocious, and downright bad public speaker, all you need to do is to follow these simple rules, and you'll be widely known as the worst speaker by anyone in your audience. Keep it up for a few speeches, and nobody will ever ask you to speak again! (Or, you could do the exact opposite of what this article says, and you'll end up giving a fairly solid, well liked speech. Why you would want to do that, I don't know, but the possibility is there if you want.)