With regards to knife-fighting:
If you ever meet a knife-fighter in the street, turn and run, or give him what he wants (but make sure he's not going to throw his knife at you). Unless, of course, you've got a bigger knife than he does, and you know how to use it without dancing around like whirlybird.
If your teacher does not tell you this the first time he hands you a knife to practice knifefighting, then look for a new teacher, or take his knifefighting propaganda with a grain of salt.
Mine scared the living hell out of me that first day. He showed me just what could happen in the blink of an eye--and you'd never even see the knife in his hand. He made very small motions. Nothing big or fancy. The forms he taught were big and fancy, but the actual apps in the forms were very controlled and slight. From then on, I've seen a lot of sloppy knife fighters here and there, often many with very little practical training. Practicing knife disarms is alright, b/c most people will try to stab or slash you in about 3 different ways. But a knifefighter will make really small motions, quick cuts you can't really block without getting sliced up. But it's rarely stab and block=disarm. Sometimes he'll use the knife so you react to it with your common-stock-2-handed-disarms, then he'll hit you with a punch so that you reel back, so that he can slice you the hell up like a pack of ground beef.
I'm alright with a knife--not great. But I'm good enough to know that you can't rely on your average disarms. Most are too complicated anyways, or require the use of two hands (never a good idea).