Favorite time an actor wasn't "Faking It"

In the Punisher (2004) Frank Castle played by Thomas Jane fights a man known as The Russian played by Kevin Nash. The scripted scene had Thomas stab Kevin with a butterfly knife and Kevin shrugs it off because he's just so tough. The hitch is that Kevin Nash really is that tough, because that knife wasn't a prop. Thomas really did accidentally stab WWE wrestler Kevin Nash in the chest, and he really did smile his way through it.

I'll be expecting a few Leonard DiCaprio in Django or Jennifer Jason Leigh in Hateful Eight stories (what is with Quentin Tarantino and on set accidents?), but I'm looking forward to some cool stories.