What does merry yarn means?

"Merry yarn" is not a commonly used phrase in English. It's possible it's a:

* Misspelling: Perhaps the intended phrase is "merry yarn," which means a cheerful or amusing story.

* Regional slang: It might be a phrase specific to a particular region or community.

* Figurative expression: The speaker could be using "merry yarn" as a metaphorical term, where "yarn" represents something like a conversation or a story.

To better understand the meaning, please provide more context:

* Where did you hear this phrase?

* Who said it?

* What was the conversation about?

With more information, I can provide a more accurate interpretation.