I remember back in junior high, my cousin brought my sister and me to a Halloween haunted house. Knowing that I was there to get scared and startled, nevertheless, when the first guy wearing a Freddy mask popped out and yelled at me, I clocked him right in the nose. It was total reflex, and I felt really, really crappy about it immediately afterwards, but it really was complete reflex.
The same guy jumped out and tried to scare me again later, and when he saw it was me, he was the one that got scared and retreated back into his hidey-hole. Poor guy.
If this guy jumped out at me when I'm walking with my wife and newborn in public, I wouldn't be surprised if I took him down. Dunno if I'd pull a gun on him (assuming I'm packing), but a takedown is definitely not out of the question. Might be good footage, too.