A less offensive form of the word "idiot". It describes a person that is silly in nature or that has done something to command being described by a slang term. For extra effect, can be said using a Scottish accent.
"Wow, look at that fucking yarby up there asking the bus driver for directions. I hope he gets sodomized with a rake at some point in his life."
"Damn, man...you've really become quite the yarby eh? You can't even spell your own fucking name."