people are impervious to pain in a street fight for various reasons. Some people even wear groin cups. "
Well relying on any kind of striking is out then. So much for all the muay thai and boxing I've done.
Really though, groin strikes tend to work very well, unless you hit like a 12 year old girl. Often not fight ending but it'll certainly get a person's a teention. That's usually enough to follow up with something more likely to fully disable someone. The worst that could happen "Well that didn't work, lets try hitting the stomach". Sometimes the goin is all that's open. Whatever is there, hit it hard and hit it repeatedly.
Personally I prefer the nose but I like groin shots too. Doesn't really matter if you hit hard.
Seriously though, if a guy is coming at you and he looks hopped up on drugs or something, not much of any martial arts is likely to work, grab the nearest available weapon. Survive first, deal with the law later. Hard drugs should be considered deadly weapons. I've heard of guys who looked completely gone with various things taking multiple gun shots and continuing to fight. Yeah like any unarmed fighting is really going to work.