Paraprosdokian: "Figure of speech in which the latter part of a sentence or phrase is surprising or unexpected; frequently used in humorous situations." i.e. "Where there's a will, there are greedy relatives."
Here are eight -- sent to me by my friend, Al Prentice:
1. Do not argue with an idiot. He will drag you down to his level and beat you with experience.
2. The last thing I want to do is hurt you, but it's still on my list.
3. Light travels faster than sound. This is why some people appear bright until you hear them.
4. If I agreed with you, we'd both be wrong.
5. Knowledge is in knowing that a tomato is a fruit. Wisdom is not putting it in a fruit salad.
6. Nostalgia isn't what it used to be.
7. Change is inevitable, except from a vending machine.
8. Evening news is where they begin with "Good Evening" and then proceed to tell you why it's not.