Maybe this is the issue. What's your job as a bouncer? It's not really self defense (meaning escape). Yes someone may try to assault you BUT your "job" is break up a fight, restrain people, "escort" them to the door etc. A strong slap, even to the ear, may be of limited in use BUT if you are just looking for a moment of shock so you can run it has a level of effectiveness. The more I have been thinking about this, especially after reading what @Brian King wrote (and he and @gpseymour can correct me if I am wrong) is that yes, self defense should teach prevention and avoidance. Yes it should teach easy to digest and repeat techniques, the focus of which is to create an opening to flee or create/maintain distance until help arrives. BUT it's also there to simply help the person gain a level of confidence, to be able to push through the instinct to curl into a ball either due to timidity or trauma.