Blindfold Boxing. But here's the twist. Match the biggest against the smallest by (fixing) drawing their names out of the hat.
Then after they are blindfolded pull the small one out and replace him with a confident un-blindfolded pugilist (boxer - not a dog). That way the confident boxer can keep out of the way of the swinging big guy and punch him, lightly in the back etc. If it's done properly it's so funny, especially if you have two or more rounds putting the small guy back on the stool between rounds where they are unblindfolded!
You make your own ring from chairs etc.