What's your one line comeback to the slap, that's better than what Chris came up with
"Fiddy slaps harder than that"
"If he's going to break the 6 foot rule, he could at least wear a mask"
"Did I just get Cuck slapped?"
C Rock - (puts on sunglasses, takes out small pen and holds up to camera) "THIS is called a neuralizer, so I need everybody in the audience and watching on TV to look directly at it"
This line would have probably won the audience over, and calmed down Will Smith enough and might get him to smile, thus diffusing the entire situation.