Similar to a backseat driver or a backseat gamer.
One who perhaps is partaking in a beta of a computer game or piece of software and tries to advise the software development team on how the software should be written or repaired.
Basically an 'end user' who is not part of the company but has been asked for an opinion or recommendation about the software but then tries to go too far and gives advice on more than he was asked for.
Admin: "Sorry guys but we're working on a fix for the multiplayer problems, there'll be a server reset in 30 minutes"
User: "What was the problem? Did they forget to open the ports? Did they have to update the firmware? Was it a malloc() issue? Did they forget to re-route it via the proxy? Did they forget a header file? Did they integrate the right settings for UDP traffic?"
Admin: "Please, we don't need any backseat coders :) just wait like everyone else"
User: "Aww, I was only interested"