Ok, so last weekend I had a small party. I live in a duplex and my downstairs neighbor is a very good friend of mine. She and her boyfriend were at my party. Everyone who was there brought their own alcohol. After the party was over and I woke up in the morning, my neighbor and her boyfriend came up to my apartment claiming that something had fallen from our deck during the party and put the tiniest dent ever on his car (seriously, it is the size of a pea). My husband went down to the driveway to look around and the only thing that was broken near my neighbor's boyfriends car was a beer bottle... and the only person that had been drinking that particular beer was the boyfriend. Furthermore, I had 4 witnesses tell me that they had seen the boyfriend throwing bottles off the deck into the woods.
My neighbor and the boyfriend are claiming that it is our responsibility to pay for the damage. I disagree. What do you think?

I think, without a witness or the actual item that supposedly fell, they would have a hard time proving you or anyone at your party had anything to do with dent.

Northwind is correct. There is no proof how or when the damage occurred. Ergo responsibility can't be assigned. I had a similar deal with a rental car a couple of years back. There was a very slight ding on the rear behind the wheel. You could only notice it if you looked at a certain angle. Since I was not hit by anyone while in the car, it must have happened in a parking lot. But the car was in my possession so I was responsible.

There's really no way to ascertain what caused the damage. It could have been done weeks ago. I don't see you being responsible. If it's really as minor as you suggest then what's the big deal anyhow? Try talking with your neighbor. If she really is the friend you say she is then you certainly ought to be able to reason with her and not let a molehill become a mountain.