As already said, the rest of us tap :)
I've never been knocked out in a tournament or in class but been hit there plenty of times. The other saturday I was rolling and my friend was demonstrating a triangle choke after you gift wrap someone.
Anyway it was on tight and there was no choking but I knew (as everyone else does) that my brain wasn't getting blood to it ... however never being choked out I left it for a few more seconds just to feel what it was like.
Soon as I felt like I was starting to go under (3-4 secs) I tapped and all the blood came back and I had a head rush. Interesting feeling and I guess I got my answer.