This scene from The Beyond, an Italian Horror flick, always cracked me the fuck up. Not even a stunt double so I don't know if it qualifies but the switch to the prosthetic head is really funny especially how it doesn't react whatsoever to...being eaten by spiders...and then the wounds are even inconsistent from shot to shot.
Caution: gore and spiders!!!
I found the fake spiders on sticks more hilarious than the dummy head in that scene.