One game - Penn State '02.
My brother was in the Navy, stationed in Norfolk, VA, flew me up there, and we drove up to State College (highways in the Northeast are MUCH different than what we have here). Right off the bat, we were treated horribly. I can understand the boo birds as we walked by in our red, but there were people calling us any and every cuss word you can think of. They threw empty, and not so empty beer cans at us, and this was common all around the stadium.
Then, of course, we know how the game went. By the time Lord threw the pick 6 in the 3rd quarter, the whole stadium was in a frenzy, and several different people were getting in my face, just inches away, screaming 'YOU SUCK!' over and over and over.
My brother ran over to get in their faces, but I held him back, because I knew even they were all plastered, there were a lot more of them than us. As were were surrounded by beligerent drunk PSU fans, a security guard grabbed us both by the arm and drug us to an upper concourse, and suggested that we either leave, or put blue on. We chose the first option, being heckled outside all the way to our car. Luckily, it didn't have Nebraska plates, so they left it alone.
So yeah, that's why we left early. Other than that, I've never left a game early, nor shut one off before it was over, including '04 Texas Tech, '07 USC, '07 and '08 Missouri, etc. The good news is that with Pelini in charge, the ballooned scores will only be in our favor.