I'm not saying it's completely ineffective, you just might want to pair it with something else like a palm to the nose in a live situation where adrenaline's running high. Take no chances.

I help teach at my martial arts place. Part of my job's teaching self-defense with real-world situations in mind.

It's also my excuse for being really really anal about stuff like this to the point of being an asshole. And my excuse for being exhausted at just past midnight when my FUBAR sleep cycle would tell you I'm normally fine and coherent.