So then the guy looked a little miffed, and asked me to show MY skills defending a knife attack. (Bear in mine, I don't train to defend knife attacks, because knife fighting is about the stupidest most dangerous thing you can do in my opinion) So I took off my shirt to use as a shield (a variation of the medieval cloak & dagger fighting style, because I'm a super nerd when it comes to all things combat related that work in real life... also my neighbors in college ran a medieval sword fighting club), he stabbed, I caught the blade in the shirt, then shoulder locked him. He demanded a redo, of course, then another and another, similar results, different finishes each time. Number of times I got stabbed = 0.
I don't teach self defense. I'm not a self defense instructor. The vast majority of what's peddled as "self defense" is certifiable nonsense. I have yet to meet a self defense instructor or see a self defense system that I feel confident in recommending to anyone. Self defense isn't about winning, it's about running away and surviving. Fighting a knife wielding maniac with your bare hands isn't self defense, it's taking a massive risk (even if you are a master of 16th century weaponized haberdashery)
It always astounds me how few self defense instructors will even remotely suggest the idea of arming yourself. (You don't need a weapon, you just need to buy their unstoppable "system"!) Even a shirt, a rock, or handful of dirt as a weapon is 100% more effective than no weapon at all when confronted with an armed attacker.