As I teach, I thought perhaps this would be an area in which I could provide a bit of suggestion. While my comments are certainly not definitive, I believe they might provide the necessary framework from which you can progress.

1.) Audience recognition: while our opinions on the religious members of our species may range from the disdainful to the outright hostile, it is necessary to remember that not all of them are congenitally stupid. With this ion mind, it is incumbent on you to ensure that your lecture is neither frivolous nor superfluous: rest assured, their are people who are simply waiting for you to make an intellectually incongruent statement- get your lecture reviewed by someone whose cognitive skills you respect.

2.) Speaker validation: you MUST find some common ground with your audience; be it the standard "lapsed christian" or the more prescient "truth seeker," you need to establish a rapport with the audience that transcends currently held beliefs.

3.) Subject-matter veracity: I will be plain in this instance: you CANNOT make any scientific mistakes; your words must be documented by hard evidence- the lack thereof is a prime entry point for the theist to question your "facts."

4.) Speaker applicability: while I was amused at your proposition to pull a "Hitchens" on your audience, this would do more harm than good. Truth be told, the unfortunate majority of our christian brethren view us as drunken rapists whose only goal is the downfall of the nation; to present a sober, intellectually valid point of view increases the impact of our message.

As to the content of the lecture, may I suggest a macro-to-micro approach; you mentioned the inefficacy of the definition of rational in the dictionary; perhaps this serves as a starting point: in a tri-partite format consider...

A.) Define rationality.

B.) Describe the lack of relationship between rationality and organized religion.

C.) Describe atheism as the alternate path that favors rationality over superstition.

Hopefully, this provides a framework from which you can work. I wish you the best of luck, and I am eager to hear how the speaking engagement ensues.

What of jokes did you make about Unitarian Universalists? I can well consider myself being one, because they're such a church equivalent of zero negative blood type And they can tell jokes about themselves, it's something I admire.

It is well possible that there will be atheists in the audience, they can be found in some congregations. As it seems from UU tradition in my country (pre-WW2) these people are not stupid, they take their church as a symbol of tolerance and higher intellectual or moral standards.
Majority will of course be "spiritual" of some kind, but they have keen minds. They should react well to some popular science. Then some general principles of interpreting evidence, like Occam's razor plus some interesting examples of debunking stuff. You could also get some shots at creationism, ingoring evidence for evolution and logical fallacies commonly used for that.

Basically, as a regular listener of skeptical podcasts I say it should be like one-man skeptical podcast

So Unrepentant, you see the situation that I am in. I don't really know my audience and for that matter, I am given to understanding that they are all over the place as far as, well anything at all.

It is going to be really hard to connect with them unless I stick strictly to well established facts. That is why I went with the idea of measuring the size of the earth. It happens that another mod (BobSpence1) lives a few miles from the tropic of Capricorn. If he is willing to help, I may be able to get a decent video out of the deal that can be used here.If I can show my audience that the world happens to be 22,000 miles around, then I can make a point about the fact that science is not about “the verdict of science” so much as it is about getting close enough to ask more questions.

As far as the whole pulling a hitch thing goes, that was really random musing more than anything. I could just as easily show up with the Gene Simmons dragon makeup and drool blood for the same pointless effect.

What I am really looking for is any ideas about how I can get a presentation going that will be useful.

>>>>>>>>>>>>>>>>>>>>>>>>.

Also, @luminon:

A Unitarian Universalist boy was out playing when he skinned his knee. So he went home to see daddy.

When he got there, his daddy said that he needed to clean it with alcohol.

So the boy says “Daddy, will it hurt?”

Daddy says “Of course not son.”

The kid then says “Are you sure?”

Daddy replies: “Son, if I was sure of anything, I would not be a Unitarian Universalist.”

1945, all of our resources are depleted from fighting WW2. Nukes are something that we can do once every several weeks.

The generals who did the Europe thing want to take out the Soviets.

Wow! Gee!

I am happy for them but have they considered if this is even possible?

While I have great respect for what General Patton did, is it even close to rational to make this specific crap shoot when failure is certain?