The term derives from the process of "rendering" in which is most known from final cut. The rendering process is slow and makes your computer lag like a bitch, thus when you are doing multiple things on the computer, your getting "render fucked"
Guy 2- I cant, i have final cut, motion, color, 12 tabs on safari, and i tunes running at the same time. Im getting render fucked
Guy 1- well then quit a few of your tabs.
Guy 2- no