To promote the freedom of expression of an individual.
This saying is often invoked in response to an insult or threat, used as a means of bypassing an altercation that will go nowhere. It can be utilized effectively to underscore the immaturity of the instigator or "wise guy" who initiated the exchanged, and ultimately concludes in the pwning of fools.
A phrase originated in your friendly neighborhood Publix supermarket. When you eat chipotle or taco bell and you have major gas you ask to fart in someones mouth to avoid the spread of a potentially horrid scent.
When someone wants to be treated a certain way, they say: “fart-treat me like that.” The “fart” before “treat” creates a cute tone of playfulness. It can also be used in sexual contexts.