Thanks to my youngest brother, I have been introduced to praprosdokianisms, or paraprosdokians. We all actually have run across them; we just didn't know the ten dollar word for these delightful little humor bits.
A paraprosdokian (from Greek "παρα-", meaning "beyond" and "προσδοκία", meaning "expectation") is a figure of speech in which the latter part of a sentence or phrase is surprising or unexpected in a way that causes the reader or listener to reframe or reinterpret the first part. It is frequently used for humorous or dramatic effect, sometimes producing an anticlimax. For this reason, it is extremely popular among comedians and satirists.(from the Wikipedia article, which then offers the lucky reader a lovely list of fun ones with attributions). But from the list my brother sent me, which has different ones, I offer some that are relevant to my librarian readers:
Some paraprosdokians not only change the meaning of an early phrase, but also play on the double meaning of a particular word, creating a syllepsis.
To steal ideas from one person is plagiarism. To steal from many is research.
Knowledge is knowing a tomato is a fruit; Wisdom is not putting it in a fruit salad.
Light travels faster than sound. This is why some people appear bright until you hear them speak.
A bus station is where a bus stops. A train station is where a train stops. On my desk, I have a work station.
You're never too old to learn something stupid.
Do not argue with an idiot. He will drag you down to his level and beat you with experience.