5 Rules for How to Write a Classic One-liner Joke

I'm a psychologist, not a professional comedy writer (After all, how funny is this first sentence?). But when, about 20 years ago, I took up to an hour each day (and I mean, for 365 days) just to write jokes, gags, and one-liners for cartoonists, comedians, and speakers, I thought I was clever enough to make it a life-long habit.
It was fun, I learned a lot, and I even sold a few jokes. However, by the end of the year my ability to keep cranking them out disappeared and I burnt out.
The experience taught me 3 things: First, I'm not cut out to be a full-time comedy writer. Second, I developed a strong appreciation of the professional comedy writers who can do this day after day, year after year. And third, I did learn how to put together a one-liner. I have used this knowledge ever since in speeches, meetings, other writing projects, and social conversation.
I have come to the conclusion that it ain't rocket science. If I can do it, you can do it (provided that you have a good sense of humor, a facility for word-play, and nothing better to do).
Before I give you my magic formula, I should tell you that formulas don't work. A great one-liner, like any work of art, has its own unique inspiration, follows its own unique rules, and surprises us in its own wonderful way. Also, the jokes I will use as examples are original (not particularly funny, but certainly original). That's because I don't want to get sued, especially by some comedian who claims I was stealing his or her jokes.
So here are 5 rules for creating a one-liner:
RULE 1: Choose 2 topics-1) the content of the joke, and 2) the surprise topic. For example, let's say you've been putting in a lot of overtime at the office. Now, just for the sake of making this a good mental exercise, let's also say that you combine this topic with the fact that you have a dog. Here is one possibility of combining them: "I've been putting in so much overtime, that I came home to an empty house last night. I found a note. It said, 'I can't take it any more. I've gone for a long walk in the park to think over our relationship.' It was from my dog."
Ok, so it's not that funny. That brings us to...
RULE 2: Look for opposites, especially ridiculous and impossible opposites. Many, many great jokes rely on opposite meanings. A few years ago at a Rotary meeting in which I ended the year of my presidency, I wanted to say a few things before turning the club over to my successor. I began by saying, "Before I formally hand over the reins of powerlessness, ..." It got a nice laugh.
RULE 3: Build up the joke in a certain direction, so that the listener is locked into one assumption, and then spring the joke on them. For example, talk as if it is something important, and end with something trivial: "I should like to introduce my business partner, my mentor, my best friend, and a man to whom I owe five bucks, ..."
RULE 4: Put the key word or phrase, the one that changes the meaning, at the very end of the one-liner. You'll notice that the very last words in the previous three jokes ARE the joke (dog, powerlessness, five bucks). Imagine a cocktail party. Everyone has a drink in his or her hands, except for one guy. His wife turns to him and says, "You know, George, you really SHOULD have something to drink--otherwise people will think you're an alcoholic." This is a lot funnier than, "You don't want people to think you're an alcoholic, do you? You'd better drink something." This second line isn't as funny because the second topic (alcoholism) is introduced before the end. It blunts the surprise and therefore the comic shock at the end.
RULE 5: Get rid of every unnecessary word and idea. Nothing ruins a one-liner more than even one extra word. My wife, Christine, is a Paramedic with the Chicago Fire Department (She was my hero long before September 11th). She works a 24-hour shift. Over the years I've developed a stock response to people who ask me if I'm worried about my wife being in the firehouse all night with all of those men: "Gee, you're right. I'd better call and warn those guys." Is there one unnecessary word in that response? I don't think so.
So there it is. Follow these rules, and you can create a one-liner. Will it rise to the level of a Henny Youngman, a Jay Leno, an Ellen DeGeneres, a Bob Hope, a Richard Pryor, or a George Carlin? Probably not, but it's fun, it's creative, it's a good mental exercise, and--who knows?--you may discover that you have a talent for it.
Oh, and one word of caution. If while you are following these rules you think of something truly funny, forget the rules. Go for what's funny.