Chiasmus

"Ask not what your country can do for you—ask what you can do for your country" - President J.F.K.

"Fuck the state pen, fuck ho's at Penn State" - Notorious B.I.G.

Chiasmus is a literary technique for structuring sentences in which two or more clauses are switched. Chiasmus are memorable and tend to stick in the listener's head. They are often employed for non-nonsense advice and folk sayings, like "when the going gets tough, the tough get going" and "what counts isn't the size of the dog in the fight — it's the size of the fight in the dog."

The structure of chiasmus is A B B A. Although usually the letters correspond to words, they can also refer to sounds as in "I’d rather have a bottle in front of me than a frontal lobotomy." Chaismus can also be achieved by reversing the meaning of clauses without changing the word order as in "never kiss a fool or let a kiss fool you."