It's very annoying to try stabbing past a teammate and have it kill them despite the fact that it really shouldn't, or killing a teammate next to you because you were standing too close when you were stabbing. From what I can understand, the end of the weapon typically has collision while the rest of it doesn't seem to as much, so you can stab "around" a teammate or a wall even if you are directly behind it. I think that the more you turn the stab the more likely it is to bounce, though.
The 180 stabs as far as I know are not really 180 stabs, but people chambering an attack, turning around, and THEN stabbing, not stabbing then turning around. They work because of the weirdass hit detection. If you are on terrain (not on an object such as a castle wall or something) people can stab into the ground, then aim upwards so the weapon connects with you and deals damage since the weapon has some velocity (if they stabbed directly at you it would immediately bounce and stun them for 3 seconds or so). I don't understand it completely though, since as mentioned before, you can be standing next to a teammate and have the part near where you are holding the weapon completely decimate them, yet overhead swings tend not to hit them at all (except on the backswing, where it will rape the shit out of them, yet only mildly annoy enemies)
What I usually do if I want to stab past something is stab to up upper right, then bring it down past the obstacle. It's mainly since there's only one stab animation, you can't stab from anywhere above your waist, making it hard to naturally stab over things you normally would be able to.
