A brand new word for you to learn!
Paraprosdokian: (noun) a figure of speech in which the latter part of a sentence or phrase is surprising or unexpected; this is frequently used in a humorous situation.
For example: "Where there's a will, I want to be in it."
Here are a few more for you...
"The last thing I want to do is hurt you. But it's still on my list."
"Light travels faster than sound. This is why some people appear bright until you hear them speak."
"If I agreed with you, we'd both be wrong."
It seems to me, Paraprosdokian, is just a fancy word for: "a funny t-shirt"