I might have known wrestling was fake back in the day, but as things like Owen/Austin SSlam97 and other such in-ring injuries have told us, not everything is fake. When he kicked him and Shawn's eyes just glazed over and he went down like that, I really thought I saw something go horribly wrong. The way they followed up on it added fuel to that fire, and only years later when I started running around the internet did I learn how it was all a work.
"Tell Me A Lie" still rules though, I don't care if it was done as a work. It's awesome.