The word “yfn” can be unfamiliar to most people, especially those from non-English-speaking countries. This slang word is widely used in these countries as an expression.
This abbreviation means something that is not appropriate for this site, so we won’t discuss it. But the other definition is “your friendly neighbor,” which means literally the word itself.
“We should invite Ben, our yfn, over for new year’s dinner.”
“I’m Jack, your yfn. Welcome to the neighborhood.”