Honestly, probably not.
While I have a significant size and strength advantage (I'm a solid 100lbs heavier), I imagine my cardio would be shot in a matter of minutes. Plus, being somewhat muscle bound makes the mechanics of kicking and punching difficult.
When I was younger and actually trained martial arts in lieu of bodybuilding, I probably could have held my own, but would still favor CM punk by a wide margin.
People like to rag on the guy, but at the very least, he is physically fit (which puts him ahead of 90% of the adult population). That, coupled with a couple of years of grappling and striking, would probably mean he wrecks most non trained people.
Either the demographic of Sherdog is full of young, athletic martial artists, or people are grossly overestimating their own abilities.