The origins of this word goes back to an episode of Comedy Central's South Park. In the episode depicting tolerance in the aptly named Museum of Tolerance, the boys find what appears to be a sterotypical Mexican sleeping on the job in wax form. However, they accidentally rouse him. This is where the word is born. He says, "Isotired buay". It was started by I in its informal manner when I said my friend was always sotired. Since then, anyone across the whole state of Texas, Mexico, and the Continental USA uses this term.