"You ker?" I've heard it in Oblivion and Futurama, what's it mean?

[John Lennon]

I'm not even 100% on if I even spelled it right, but I've heard it a lot in The Elder Scrolls IV: Oblivion, and even used by Bender in Futurama, calling Zoidberg a "Ker"
Anyone have any idea on it's definition?