Is a McSlap the best form of self-defense?

By now this video has done the rounds of a guy getting his just comeuppance in culturally enriched Manchester (England).

But this whole video is making me question my martial arts training. Rather than punching someone in the face, having them fall and bang their head; is the best way forward not a little stunning slap?

Is a McSlap the best form of self-defense?
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