Where do these phrases get started?

[Arkitech]

You ever wonder who's the person to originally coin some of these phrases you hear

For example was it a pimp who came up with the phrase "bitchslap"?

Who came up with the phrases choking your chicken, slappin your monkey or beating your donkey? This obviously had to be the product of a S&M freak with an animal fetish

 

[killface]

It's just a matter of someone making something up and the word spreading. Alot of them start on college campuses, because with such a tightly knit population, there is plenty of opportunity for words to get around. When college kids visit or talk to kids from other colleges, the words spread.
My friends have done it a number of times, but the haven't spread all that much (since we weren't in college at the time) such as the term "welf" short for welfare - "Our TV is so welf, it only goes up to channel 13."
As William S. Burroughs said - words are a virus. Their only function is to replicate themselves.