I was a self defense instructor and I have seen guys get kicked in the groin and BLEED and not pass out because they were high on drugs!

Its just pain! Yes it will work 99% of the time IF you get a direct hit there...but (and this is a HUGE but):

a) It harder to hit than you think!
b) It takes a few seconds ( I know this from Personal experience lol) for the pain to set it...and you could get stabbed in that time! Fast forward 5 minutes, the attacker is ok and now you have a new hole in your body!
c) MOST IMPORTANTLY....do you want to risk your attacker being that 1% that doesn't feel it because he is high??

So like I said b4 its a tool....I never said NEVER use it...i'm just cautioning against RELYING on it as "THE" trick that will save you all the time.

Stay safe all.

Perfection does not exist. The question therefore, is: what level of imperfection are we willing to settle for?