MightyEInherjar
Two Ravens Above Us
I have to say, I am getting pretty tired of every TKD black belt thinking they can drop every guy in the room. IMO, it might help you if you get jumped by a guy with a knife, only because you're going to be on your back foot a lot and throwing kicks (which will inevidably lead to getting stabbed in the legs..)
As well as other MMAs, I've done HACA/ARMA (basically western/european armed combat) since I was 14 years old. If someone comes at with you with a knife, and you don't have one yourself, keep your hips back, your head forward, and presuming they're right handed, your left hand out. Everybody knows someone who's either gotten a nail or blade stuck in their hand or foot...and that's essentially what you want to reenact here in a worst case scenario. There aren't any major veins or arteries in your hand, and you can always afford to get surgery to repair the damage you took taking the knife.
The aim is to grab the guy by the wrist of his knife hand, and if that doesn't succeed, take the stab to your hand to prevent damage on your body or any major organs. Sure it'll hurt like a *****, but after words you'll be alive. After you have the guy's wrist, or have taken it in your hand, the object is to either use his momentum to take the knife (which is a bunch of fancy BS that will just get you stabbed) or throw a strong right or elbow into his jaw or nose to get him to back off long enough for you to escape.
If you have a knife as well, and you're not thinking of walking away in this, take the knife in your hand or arm like mentioned, and his right where his left shoulder meets his neck will be open. Drive home the knife there, or if you can, stab him in his armpit. The combination of his lymph nodes being destroyed, possible lung puncture, and bleeding should put him out of the fight for the rest of his life.