It means "farming your own fail".

A farmer grows his own food, therefore a fail farmer grows his own fail, meaning he makes a lot of fails upon themselves.

To be called a fail farmer is an insult.
Example 1:
Guy 1: "Wow those guys over there are trying to act all cool."
Guy 2: "Wow, what a bunch of fail farmers."

Example 2:
Guy 1: "Wow these school computers keep shutting down"
Guy 2: "That's because they're a bunch of fail farmers"

Example 3:
Guy 1: "Lol, look at that fail farmer over there"
Guy 2: "Epic fail, he just fell on his face"
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