Also Warren shot Buffy and Tara.I think that if the villains used guns they could kill the slayer a lot faster and a lot easier. Like imagine if Spike had just got a gun and brought it to the Bronze with him the first time he saw Buffy he could have just shot her with the element of surprise and it would be over with since she didn't know that Spike was a vampire or that he was after her. It's probably because Spike wants more of a challenge of trying to best the slayer but later on when he was getting frustrated that he couldn't kill her he could have just got a gun and gone to the Bronze or to her school and end it quickly. So yeah that's why Darla used a gun it was a smart move on her part. I always wondered why more villains on the show didn't do that but then Buffy would have less of a chance to defeat them and there wouldn't be cool fight scenes.
True it might but it wont stop your head being ripped of which Buffy can do . Plus it bulky so it not easy to wear . Plus they would get killed by their own people who think they being a coward .I wonder if Kevlar can stop a stake to the heart? Maybe if Buffy were able to stake a vamp the Kevlar would still protect the heart from the wooden properties (as long as it didn't rip).
I just looked it up...it has fire resistant properties and gets used as armor by fencers. It wouldn't necessarily stop a crossbow bolt the same way it would a bullet, but would seem to make Buffy's job harder.
At the very least, maybe it could stop the very embarrassing death by floating pencil as happened in one ep.