A person (usually in their 20s) that moves from suburban/ rural America to any major city. Generally, these people are running away from or ashamed of their pasts and seeking to fruitlessly reinvent themselves and adhere to every possible perceived "trendy urban" stereotype ( e.g. In NYC, dressed head-to-toe in black, toting a "Manhattan Portage" bag, expensive sunglasses, etc.) making them extremely easy to spot. The phony "city" act is most obnoxious when the "transplant" has friends from their hometown visiting or they are back in their real hometown visiting.
When one removes the tobacco and cuts off the filter from a cigarette, and replaces these components with a roach and some sweet Devil's Lettuce (aka: Marijuana). A useful alternative when there are no papers available to roll a joint.
Treb: "Man, I wish we could have a joint, but we're all out of papers!"
Geebz: "Don't worry mate, if you chuck us a ciggie I'll make us a transplant."
Transplant is a broader term to describe anyone who's not originally from an area, since not all transplants are newcomers. Some have been in area for many years.
Originally, a joke from "comedian" Tom Meyers detailing an experience at a 7-11 convenience store. A customer somehow communicates to Tom that the customer had a sick friend or family member. Tom observes a customer purchasing an assortment of junk food, then his sharp comedic mind generated the punchline for this infamous joke.
"looks like someone had a bong hit transplant!" Bam! The legion was born. The advance quality and sharp mind of this comedian got the attention of the Cum Town podcast. This "joke" remains the longest recurring joke on the podcast, the r/cumtown subreddit and the entire comedy world.